Native locale_names for 14 locales + drop forced-en in editor tabs

Translates the 16-language locale_names block in zh-CN, zh-TW, ko, hi,
vi, tr, de, fr, es, pt-BR, ru, uk, it, pl to the target locale's own
language (e.g. de file: 'en' => 'Englisch', 'ja' => 'Japanisch').

DocumentEditor blade no longer hardcodes 'en' as the locale_names
lookup — falls back to the current UI locale. Test still passes
because tests run with default app locale 'en' and the en file
maps to "Japanese" / "English" etc.

A user editing in ja now sees [English] [日本語 ★] tabs instead of
[English] [Japanese ★].

docs/superpowers/specs/2026-05-09-media-manager-design.md

@@ -0,0 +1,192 @@
+# Media Manager — Design Spec
+
+Date: 2026-05-09
+
+## Goal
+
+Add a simple media manager to the admin panel so users can upload, rename, download, and delete arbitrary files (images, video, audio, PDF, ZIP) and reference them from Markdown documents by a stable logical filename or path.
+
+## Non-Goals
+
+- Folder management UI (explicit folder create/move/rename). Folders are expressed implicitly via slashes in the logical path.
+- Versioning or revision history of media files.
+- Automatic rewriting of existing Markdown when a media file is renamed or deleted (broken-link warning is left to manual operation).
+- Migration of existing `storage/app/public/images/` files into the new media table.
+
+## Core Design
+
+### Logical / Physical Separation
+
+- **Logical path** (DB-managed): user-facing identifier used in Markdown, e.g., `report.png` or `2026/spec.pdf`. UNIQUE.
+- **Physical path** (filesystem): `media/{uuid}.{ext}` under the `public` disk. Filename is a UUID; extension preserved from the original upload.
+- Renaming changes only the logical path; the physical file is never moved.
+- Deletion removes the DB row and the physical file.
+
+### Markdown Reference Resolution
+
+- Markdown reference syntax stays standard: `![alt](report.png)` or `![alt](2026/spec.pdf)`.
+- Resolution policy: **exact match only** on `logical_path`. No basename fallback, no fuzzy matching.
+- Only schema-less, non-absolute paths are looked up. `https://…`, `http://…`, and paths starting with `/` are passed through to the existing pipeline (YouTube/Vimeo/video/audio handlers).
+
+### Editor Drag-and-Drop Integration
+
+- The existing `POST /images/upload` endpoint (used by EasyMDE) is rerouted through the same `MediaService`.
+- The endpoint returns the **logical path** (e.g., `report.png`) as `data.filePath`, so the inserted Markdown becomes `![alt](report.png)` rather than an absolute UUID URL.
+- Logical-path collisions during editor uploads are auto-resolved server-side by appending `-2`, `-3`, … to the basename (max 100 attempts before erroring). Collisions in the manual admin upload form are surfaced as validation errors instead.
+
+## Data Model
+
+### Table `media_files`
+
+| Column | Type | Notes |
+|--|--|--|
+| `id` | bigint, pk | |
+| `logical_path` | varchar(512), UNIQUE | Validated: no leading/trailing `/`, no `..`, no empty segments, no consecutive `/`, non-empty |
+| `physical_path` | varchar(255) | `media/{uuid}.{ext}` (relative to the public disk) |
+| `original_name` | varchar(255) | Original filename at upload time. Used as the Content-Disposition filename on download |
+| `mime_type` | varchar(127) | Detected at upload |
+| `size` | unsigned bigint | Bytes |
+| `uploaded_by` | foreign key → `users.id`, nullable | ON DELETE SET NULL |
+| `created_at` / `updated_at` | timestamp | |
+
+Indexes: `UNIQUE(logical_path)`, plain index on `uploaded_by`.
+
+### Eloquent Model `App\Models\MediaFile`
+
+- `publicUrl()`: returns `Storage::disk('public')->url($this->physical_path)`.
+- Override `delete()` to remove the physical file before deleting the DB row. If the physical delete fails, the DB row is **kept** and the failure is logged so it can be retried.
+
+## Components
+
+### Backend
+
+| Role | File | Responsibility |
+|--|--|--|
+| Routes | `routes/web.php` (additions) | Admin resource routes for media; standalone `auth`-only download route |
+| Admin controller | `app/Http/Controllers/Admin/MediaController.php` | index / store / edit / update / destroy. Inline `validate()`; no FormRequest |
+| Service | `app/Services/MediaService.php` | `store(UploadedFile, ?string $logicalPath, bool $autoSuffixOnConflict = false)`, `rename(MediaFile, string $newLogicalPath)`, `delete(MediaFile)`. Owns logical-path normalization, collision detection, and physical I/O |
+| Listener update | `app/Markdown/MediaEmbedListener.php` | Add a Phase-1 logical-path rewrite that walks `Image` and `Link` nodes and replaces matching `logical_path` URLs with the physical public URL before the existing video/audio/YouTube/Vimeo detection runs |
+| Editor integration | `app/Http/Controllers/ImageUploadController.php` | Rewritten to call `MediaService::store(..., autoSuffixOnConflict: true)` and return `data.filePath = <logical_path>` |
+
+### Frontend
+
+| View | Content |
+|--|--|
+| `resources/views/admin/media/index.blade.php` | Search box, inline upload form, paginated table (logical path / type icon or thumbnail / size / updated_at / actions). Actions: rename, download, delete |
+| `resources/views/admin/media/edit.blade.php` | Rename-only form (edits `logical_path`) |
+
+Navigation entry added to `resources/views/layouts/navigation.blade.php` under the admin dropdown.
+
+### Routing
+
+```php
+Route::middleware(['auth', 'admin'])->prefix('admin')->name('admin.')->group(function () {
+    Route::resource('users', AdminUserController::class)->except(['show']);
+    Route::resource('media', AdminMediaController::class)->except(['show', 'create']);
+});
+
+Route::middleware('auth')->group(function () {
+    // existing routes...
+    Route::get('/media/{media}/download', [AdminMediaController::class, 'download'])->name('media.download');
+});
+```
+
+Rationale: CRUD is admin-only; download is reachable by any authenticated user (so document readers can grab attached PDFs/ZIPs). The physical file under `/storage/media/{uuid}.ext` is already publicly readable via the public disk — the `download` route only adds the `original_name` Content-Disposition.
+
+## Data Flow
+
+### Upload (admin form)
+
+1. `POST /admin/media` (multipart) → `MediaController::store`
+2. Validate: `file` required; allowed MIME (image jpeg/png/gif/webp/svg, video mp4/webm, audio mp3/m4a/ogg/wav, application/pdf, application/zip); `max:102400` (100 MB); `logical_path` optional.
+3. `MediaService::store($file, $logicalPath, autoSuffixOnConflict: false)`:
+   - Normalize logical path (trim, reject `..`, reject leading/trailing `/`, reject empty/consecutive segments, default to `original_name` if blank).
+   - Check `logical_path` UNIQUE; on conflict throw a validation exception.
+   - Save physical file to `media/{uuid}.{ext}` via `Storage::disk('public')->putFileAs`.
+   - Create the `media_files` row with `uploaded_by = auth()->id()`.
+4. Redirect to `admin.media.index` with a success flash.
+
+### Rename
+
+1. `PUT /admin/media/{media}` → `MediaController::update`
+2. Validate the new `logical_path` (same normalization + UNIQUE excluding self).
+3. Update the DB row only. Physical file is untouched.
+4. **Side effect**: any existing Markdown referring to the old logical path becomes a broken link. No automatic rewrite in this iteration.
+
+### Download
+
+1. `GET /media/{media}/download` → `MediaController::download` (auth-only).
+2. Returns `Storage::disk('public')->download($physical_path, $original_name)`.
+
+### Delete
+
+1. `DELETE /admin/media/{media}` → `MediaController::destroy`
+2. `MediaService::delete($media)`: try to delete the physical file; on success delete the DB row. On physical-delete failure, log it and surface a warning flash; the DB row is preserved so the operation can be retried.
+3. Existing Markdown references to the deleted file become broken links. No warning surfaced in this iteration.
+
+### Markdown Render-Time Resolution
+
+The `MediaEmbedListener` walks both `Image` and `Link` nodes during `DocumentParsedEvent` in two ordered phases:
+
+**Phase 1 — Logical-path rewrite** (new):
+For each `Image` or `Link` node, take its URL.
+- If the URL has a scheme (`http(s)://`, etc.) or starts with `/`, skip it.
+- Otherwise look up `MediaFile::where('logical_path', $url)->first()`.
+- On hit, replace the node's URL with `$media->publicUrl()` (e.g., `/storage/media/{uuid}.png`). The node type is unchanged.
+
+**Phase 2 — Embed detection** (existing, unchanged):
+The existing `MediaEmbedListener` logic runs against the (possibly rewritten) URL. `Image` nodes whose URL ends in a video/audio extension or matches YouTube/Vimeo get replaced with a `MediaEmbedNode` rendered as `<video>` / `<audio>` / iframe. Everything else falls through to CommonMark's default rendering.
+
+Net behavior:
+- `![alt](report.png)` → image extension, no embed rewrite, `<img src="/storage/media/{uuid}.png" alt="alt">`.
+- `![](demo.mp4)` → URL rewritten to physical, then video extension detected, replaced with `<video>` tag.
+- `[manual](manual.pdf)` → Link node, URL rewritten to physical, CommonMark renders `<a href="/storage/media/{uuid}.pdf">manual</a>`.
+- `![](https://example.com/foo.png)` → has scheme, Phase 1 skips; Phase 2 also has nothing to do; CommonMark renders default `<img>`.
+
+`MediaUrlResolver` itself stays focused on URL→embed-HTML mapping for video/audio/YouTube/Vimeo (i.e., its public surface does not change). The logical-path rewrite is a separate concern handled in the listener.
+
+### Editor Drag-and-Drop
+
+1. EasyMDE → `POST /images/upload` (existing endpoint).
+2. `ImageUploadController` calls `MediaService::store($file, null, autoSuffixOnConflict: true)`.
+3. Response: `{ data: { filePath: <logical_path>, altText: <basename without ext> } }`.
+4. EasyMDE inserts `![<basename>](<logical_path>)` into the Markdown.
+
+## Validation & Error Handling
+
+| Case | Behavior |
+|--|--|
+| Invalid logical path (`..`, leading/trailing `/`, empty/consecutive segments, > 512 chars, empty after trim) | Validation error |
+| Logical-path collision (admin form) | Validation error: "同じパスのファイルが既に存在します" |
+| Logical-path collision (editor D&D) | Auto-suffix `-2`, `-3`, … up to 100 attempts; on exhaustion return a 422 |
+| Disallowed MIME / extension | Validation error |
+| File over 100 MB | Validation error. `php.ini` `upload_max_filesize` / `post_max_size` must be ≥ 100 MB; document this as an environment requirement |
+| Physical-delete failure | Log + warning flash; DB row kept |
+| Deleted/renamed media still referenced in MD | No warning; the resolver misses, the link renders as a broken link |
+| Markdown URL is absolute (`http(s)://`, leading `/`) | Resolver passes through to existing video/audio/YouTube/Vimeo logic |
+| Authorization | All CRUD under `auth + admin` middleware; download under `auth` only |
+
+## Testing
+
+PHPUnit feature tests using a fake `public` disk so real file I/O is exercised in temp storage.
+
+| Test | Coverage |
+|--|--|
+| `MediaServiceTest::store` | with explicit logical path, with default (original name), conflict rejection, invalid-path rejection, `uploaded_by` recorded |
+| `MediaServiceTest::rename` | DB updated, physical file unchanged, conflict rejection |
+| `MediaServiceTest::delete` | physical + DB removed; on physical-fail DB row kept |
+| `MediaServiceTest::auto_suffix` | editor path: `report.png` collision → `report-2.png` |
+| `Admin\MediaControllerTest` | non-admin → 403 on index/store/update/destroy |
+| `MediaDownloadTest` | unauth → redirect/401, auth → file with `original_name` |
+| `MediaEmbedListenerTest` (extended) | logical-path hit rewrites Image/Link URL to physical; miss leaves URL untouched; absolute URL (with scheme or leading `/`) skipped |
+| `DocumentRenderIntegrationTest` | `![](report.png)` rendered to `<img src="/storage/media/{uuid}.png">` after a `MediaFile` row exists |
+
+Coverage target: the rows above. Not aiming for 100%.
+
+## Out-of-Scope (explicit)
+
+- Bulk operations (multi-select delete, bulk rename).
+- Quota/usage tracking per user.
+- CDN / signed URLs.
+- Migration of existing `images/` content into `media_files`.
+- Rewriting existing Markdown when a logical path is renamed or deleted.

docs/superpowers/specs/2026-05-10-article-i18n-design.md

@@ -0,0 +1,275 @@
+# 記事の多言語対応 + デフォルト言語フォールバック
+
+- **Date:** 2026-05-10
+- **Branch:** `feature/article-i18n`（`main` から分岐）
+- **Status:** Design approved, ready for implementation plan
+
+## 背景
+
+UI言語切り替えは16言語対応済み（`SetLocale` ミドルウェア + `users.locale` カラム + セッション/Cookie）。
+一方、記事本体（`documents` テーブル）は単一言語のまま：1ドキュメント = 1行で `title`/`content`/`rendered_html` を直接保持し、locale非対応。
+
+本設計は、記事自体を多言語化し、ユーザーのUI言語に応じた翻訳を提示する。翻訳が無ければ「その記事の原語版」へフォールバックする。
+
+## 決定事項サマリ
+
+| 論点 | 決定 |
+|---|---|
+| 翻訳のデータモデル | 1記事 + `document_translations` 子テーブル |
+| デフォルト言語 | 記事ごとに `documents.default_locale` を持つ |
+| URL | デフォルト言語のslug固定（言語非依存） |
+| 表示title | 現在locale → default_locale でフォールバック |
+| 編集UX | 1記事の編集画面に言語タブ |
+| `[[wiki-link]]` 解決 | 全言語のtitleを対象、現在locale優先の決定論的順序 |
+| 検索 | 全言語のtitle/contentを対象、表示titleは現在locale |
+| マイグレーション | 既存記事は `config('app.locale')` を `default_locale` として移行 |
+| フォールバック表示 | 上部バナー + 「翻訳を追加」ボタン |
+
+## Section 1: データモデル
+
+### `documents` テーブル（変更）
+
+| 操作 | カラム | 備考 |
+|---|---|---|
+| 追加 | `default_locale` VARCHAR(10) NOT NULL | フォールバック先となる原語 |
+| 削除 | `title` | `document_translations` へ移管 |
+| 削除 | `content` | 同上 |
+| 削除 | `rendered_html` | 同上 |
+| 維持 | `path`, `slug`, `frontmatter`, `file_size`, `file_hash`, `file_modified_at`, `created_by`, `updated_by`, timestamps, `softDeletes` | |
+
+`path`/`slug` は引き続き「default_locale のtitle」から生成。タイトル変更で再生成される既存ロジックも default_locale のtitleに連動。
+
+### `document_translations` テーブル（新規）
+
+```
+id              BIGINT PK
+document_id     FK → documents (cascade delete)
+locale          VARCHAR(10)
+title           VARCHAR(255)
+content         TEXT
+rendered_html   TEXT NULLABLE
+created_by      FK → users (nullOnDelete)
+updated_by      FK → users (nullOnDelete)
+created_at, updated_at
+
+UNIQUE (document_id, locale)
+INDEX (locale, title)                            -- wiki-link / QuickSwitcher 用
+FULLTEXT (title, content) WITH PARSER ngram      -- MySQL のみ（既存と同条件）
+```
+
+- `(locale, title)` には**unique制約は付けない**。既存 `documents.title` も unique でないため挙動互換性を保つ。代わりに wiki-link 解決順序を決定論にする。
+- SQLite（テスト環境）では FULLTEXT インデックス作成をスキップ（既存マイグレーションと同じ条件分岐）。
+
+### マイグレーション手順
+
+1. `documents.default_locale` カラム追加（デフォルト値 `config('app.locale')`、nullable=false）
+2. `document_translations` テーブル作成
+3. データ移行：既存各 `documents` 行から `(title, content, rendered_html, created_by, updated_by)` を `document_translations` に複製、`locale = config('app.locale')` をセット
+4. `documents` テーブルの旧FULLTEXTインデックス（`documents_search_index`）を削除
+5. `documents.title`, `documents.content`, `documents.rendered_html` カラムを削除
+
+`down()` は対称的に逆順で復元するが、データ復元は best-effort（複数translation存在時はdefault_localeのものを採用）。
+
+## Section 2: モデル & サービス層
+
+### `Document` モデル
+
+- `title`/`content`/`rendered_html` をfillable/直接プロパティから削除
+- 新リレーション
+  - `translations(): HasMany` → `DocumentTranslation`
+  - `defaultTranslation(): HasOne` → `where('locale', $this->default_locale)`
+- アクセサ（**現在 `App::getLocale()` のtranslation → 無ければdefault_localeのtranslation**）
+  - `getTitleAttribute(): string`
+  - `getContentAttribute(): string`
+  - `getRenderedHtmlAttribute(): ?string`
+- 新メソッド
+  - `translationFor(string $locale, bool $fallback = true): ?DocumentTranslation`
+  - `isFallback(string $requestedLocale): bool` — バナー判定用
+  - `availableLocales(): array` — タブ生成用、translation存在のlocale一覧
+
+### `DocumentTranslation` モデル（新規）
+
+```php
+fillable: [document_id, locale, title, content, rendered_html, created_by, updated_by]
+casts: timestamps
+relations: document(): BelongsTo, creator(), updater()
+scope:    scopeSearch(Builder, string)  -- MATCH(title, content) AGAINST(?)
+static:   renderMarkdown(string): string  -- Document から移管（純粋関数）
+```
+
+### `DocumentService` 改修
+
+| メソッド | 変更内容 |
+|---|---|
+| `createDocument($title, $content, $userId, $locale = null)` | `$locale` 未指定なら `App::getLocale()`。document を作成し `default_locale = $locale`、translationを1件作成。path/slug は title から生成 |
+| `updateDocument(Document $doc, $title, $content, $userId, $locale)` | 指定 `$locale` のtranslationをupsert。`$locale === default_locale` のときだけ path/slug 再生成 |
+| `addTranslation(Document $doc, $locale, $title, $content, $userId): DocumentTranslation` | 新言語のtranslation追加。重複locale時は422 |
+| `deleteTranslation(Document $doc, string $locale): void` | default_locale の翻訳は削除拒否（例外） |
+| `setDefaultLocale(Document $doc, string $locale): Document` | `default_locale` 切り替え。新しいdefault_localeのtranslationが存在しない場合422。切替後 path/slug を新default_localeのtitleから再生成 |
+| `findByTitle($title, $locale = null): ?Document` | locale指定優先。後述の解決順序を実装 |
+| `search(string $query, int $limit = 20)` | `DocumentTranslation::search()` ベース、結果documentをdistinct化 |
+| `getDirectoryTree()` | path/階層構造はdocumentレベルのまま、表示titleはアクセサ経由で現在locale + フォールバック |
+
+### `WikiLinkResolver`（新規 `app/Services/WikiLinkResolver.php`）
+
+`processLinks()` と `syncLinks()` から共通利用される解決ロジック：
+
+```
+resolve(string $linkText, string $currentLocale): ?Document
+  1. translations WHERE locale = $currentLocale          AND title = $linkText
+  2. translations WHERE locale = document.default_locale AND title = $linkText
+  3. translations WHERE                                       title = $linkText
+                  ORDER BY document_id ASC LIMIT 1
+  4. documents    WHERE slug = SlugHelper::generate($linkText)
+  5. null
+```
+
+- `Document::syncLinks()` と `Document::processLinks()` はResolver利用に書き換え
+- `processLinks()` のリンク**表示ラベル**は原文のまま（例: 英語本文中の `[[Getting Started]]` はja表示時もラベル「Getting Started」）。クリック後の遷移先記事は現在localeで表示される
+- 既存の `DocumentLink` テーブルはスキーマ無変更（`target_title` を保存しているだけなのでlocale非依存で運用可能）
+
+## Section 3: ルーティング & コントローラ層
+
+### 既存ルート（変更なし）
+
+- `GET /documents/{document}` → slug一致でdocumentバインド
+- `GET /documents/{document}/edit`
+- `GET /documents/create`
+
+URLは言語非依存。表示言語は `SetLocale` ミドルウェアが解決した `App::getLocale()` に従う。
+
+### `Document::resolveRouteBinding()`
+
+slugは `documents` テーブル直下のため既存ロジックそのまま。
+翻訳title（例: `はじめに`）でURLを直接叩いた場合は404のまま（検索/QuickSwitcher経由で見つける想定）。
+
+### 新規ルート: 翻訳の管理
+
+| メソッド | URL | 名前 | 機能 |
+|---|---|---|---|
+| GET | `/documents/{document}/translations/{locale}/edit` | `documents.translations.edit` | 既存翻訳の編集（`DocumentEditor` を再利用） |
+| POST | `/documents/{document}/translations` | `documents.translations.store` | 新言語追加 |
+| DELETE | `/documents/{document}/translations/{locale}` | `documents.translations.destroy` | 翻訳削除（default_locale 不可） |
+
+- `{locale}` は `SetLocale::SUPPORTED_LOCALES` のキーで route constraint
+- すべて `auth` + `can:update,document` ミドルウェア配下
+
+### `/` ルート
+
+`slug = home` の document を探してリダイレクト（既存通り、slugは言語非依存のため変更不要）。
+
+## Section 4: Livewire コンポーネント & ビュー
+
+### `DocumentViewer`（改修）
+
+```php
+public Document $document;
+public string $viewLocale;        // 実際に表示中のlocale（フォールバック後）
+public bool $isFallback;          // バナー表示判定
+public string $renderedContent;   // wiki-link処理済みHTML
+public $backlinks;
+```
+
+`mount()` フロー:
+1. `$current = App::getLocale()`
+2. `$translation = $document->translationFor($current, fallback: true)`
+3. `$this->viewLocale = $translation->locale`
+4. `$this->isFallback = ($current !== $translation->locale)`
+5. `WikiLinkResolver` で `$translation->rendered_html` 内のwiki-linkを現在locale基準で再解決
+
+ビュー `livewire/document-viewer.blade.php`:
+- 上部にフォールバックバナー（`$isFallback === true` のみ）
+  - 文言は `lang/{locale}/messages.php` に追加（例: `documents.fallback_notice`、`documents.add_translation`）
+  - 「翻訳を追加」ボタン → `documents.translations.store` への小フォーム（locale = 現在UI locale）
+- バックリンク表示titleは `$backlink->title` アクセサ経由（自動でフォールバック）
+
+### `DocumentEditor`（改修）
+
+```php
+public ?Document $document;       // 既存編集時、新規作成時はnull
+public string $editingLocale;     // 現在編集中のタブ
+public string $title;             // editingLocale の title
+public string $content;           // editingLocale の content
+public array $availableLocales;   // この記事で既に翻訳がある locale 一覧
+public bool $isNewLocale;         // 既存翻訳の編集 or 新規追加
+```
+
+メソッド:
+- `switchTab(string $locale)` — 未保存変更があれば確認ダイアログ、translation取得 or 空フォーム
+- `save()` — 既存ならupdate、新規ならaddTranslation
+- `delete()` — 翻訳削除（default_locale以外）
+- `setAsDefault(string $locale)` — default_locale変更（path/slug再生成）
+
+ビュー `livewire/document-editor.blade.php`:
+- 上部にタブバー: `[JA*] [EN] [zh-CN] [+ 翻訳を追加 ▾]`
+  - `*` は default_locale 印
+  - `+` ドロップダウンで未追加の `SUPPORTED_LOCALES` を選択可能
+- 既存のEasyMDE設定はそのまま流用、`wire:model` の単一入力構造を維持
+- default_locale変更UI（タブの隣にメニュー or 「この言語をデフォルトにする」ボタン）
+
+### `SidebarTree`（軽微改修）
+
+- `getDirectoryTree()` の戻り値内 `name`（path basename）はpathベースのまま
+- ファイル名表示は `$document->title`（アクセサ経由）に切り替え
+- treeのキャッシュキー（もしあれば）に `App::getLocale()` を含めて、locale切替で再構築
+
+### `QuickSwitcher`（改修）
+
+- 検索クエリを `DocumentTranslation::search()` に投げ、結果documentをdistinct化
+- 表示行は `$doc->title`（アクセサ）+ ヒットしたtranslationが現在locale以外なら小さなlocaleバッジ
+
+## Section 5: テスト計画 & 受け入れ基準
+
+### ユニットテスト（追加）
+
+| ファイル | 検証内容 |
+|---|---|
+| `tests/Unit/Models/DocumentTest.php` | `title`/`content`/`rendered_html` アクセサが現在localeを返す／無ければdefault_localeにフォールバック／`isFallback()` 真偽／`availableLocales()` |
+| `tests/Unit/Models/DocumentTranslationTest.php` | `(document_id, locale)` unique／cascade delete／`renderMarkdown()` |
+| `tests/Unit/Services/WikiLinkResolverTest.php` | 解決順序5段階すべて／同名タイトル衝突時の決定論性／slug fallback／nullケース |
+| `tests/Unit/Services/DocumentServiceTest.php` | `createDocument` がtranslationを1件生成／`updateDocument` がdefault_locale時のみpath再生成／`addTranslation`／`deleteTranslation`（default_locale削除拒否）／`setDefaultLocale`（未存在translation時422 + path再生成）／`search` のdistinct化 |
+
+### フィーチャーテスト（追加）
+
+| ファイル | 検証内容 |
+|---|---|
+| `tests/Feature/DocumentI18nTest.php` | 現在locale=ja で英語のみの記事を表示→英語版が表示されバナーが出る／ja版を追加後はバナーなし／QuickSwitcherで日本語クエリ・英語クエリどちらも同記事ヒット |
+| `tests/Feature/DocumentTranslationCrudTest.php` | 翻訳追加POST／編集GET/PATCH／削除DELETE（default_localeは422）／非権限ユーザは403 |
+| `tests/Feature/DocumentMigrationTest.php` | マイグレーション前の擬似データ→migrate実行→translationsへ正しく移行／documentsの旧カラムが消去 |
+
+### 既存テストの修正範囲
+
+- `DocumentService` を呼ぶ既存テストはfactoryで `default_locale` 指定が必要
+- `Document::factory()` は `DocumentTranslationFactory` と連動
+- 既存の `processLinks` / `syncLinks` テストは `WikiLinkResolver` 経由に書き換え
+
+### 受け入れ基準（DoD）
+
+1. UI言語をjaにして英語のみ記事を開く → 英語コンテンツが表示され、上部に日本語バナー＋「翻訳を追加」ボタンが出る
+2. 「翻訳を追加」→ 編集画面でja版を作成・保存 → 同URLを再表示 → ja版がバナーなしで表示
+3. `[[Getting Started]]` と `[[はじめに]]` の両方が同一記事へリンクする
+4. QuickSwitcherで「はじめに」「Getting Started」どちらでも同記事がヒットする
+5. 編集画面の言語タブを切り替えて、各言語のtitle/contentを独立に編集・保存できる
+6. default_locale設定の翻訳は削除できない（UIで削除ボタン非表示＋バックエンドで422）
+7. 既存の `composer test` がすべて緑
+8. マイグレーション後、既存記事すべてが `default_locale = config('app.locale')` で正しく翻訳化されている
+
+## ブランチ & コミット計画
+
+- ブランチ: `feature/article-i18n` を **`main` から分岐**（`feature/media-manager` ではない）
+- コミット粒度の目安（1 PR想定で7コミット）：
+  1. マイグレーション（`document_translations` 作成 + 既存データ移行 + 旧カラム削除）
+  2. `DocumentTranslation` モデル + factory
+  3. `Document` モデルアクセサ/リレーション改修
+  4. `WikiLinkResolver` + `DocumentService` 改修
+  5. ルート + 翻訳CRUDコントローラ
+  6. `DocumentViewer` + バナー + lang追加
+  7. `DocumentEditor` タブUI + `SidebarTree`/`QuickSwitcher` 調整
+
+## スコープ外（YAGNI）
+
+- 翻訳の自動生成（DeepL等の外部API連携）
+- 翻訳の進捗ダッシュボード（カバレッジ表示）
+- 言語ごとの別URL（`/ja/documents/...`）
+- title翻訳に応じたslugの言語別生成
+- RTL言語サポート

src/app/Http/Controllers/DocumentTranslationController.php

@@ -0,0 +1,54 @@
+<?php
+
+namespace App\Http\Controllers;
+
+use App\Http\Middleware\SetLocale;
+use App\Models\Document;
+use App\Services\DocumentService;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\Auth;
+
+class DocumentTranslationController extends Controller
+{
+    public function __construct(private DocumentService $service) {}
+
+    public function store(Request $request, Document $document)
+    {
+        $validated = $request->validate([
+            'locale' => ['required', 'string', 'in:' . implode(',', array_keys(SetLocale::SUPPORTED_LOCALES))],
+            'title' => ['required', 'string', 'max:255'],
+            'content' => ['required', 'string'],
+        ]);
+
+        try {
+            $this->service->addTranslation(
+                $document,
+                $validated['locale'],
+                $validated['title'],
+                $validated['content'],
+                Auth::id(),
+            );
+        } catch (\InvalidArgumentException $e) {
+            return response()->json(['message' => $e->getMessage()], 422);
+        }
+
+        return redirect()->route('documents.show', $document)
+            ->with('message', __('messages.documents.translation_added'));
+    }
+
+    public function destroy(Document $document, string $locale)
+    {
+        if (!array_key_exists($locale, SetLocale::SUPPORTED_LOCALES)) {
+            abort(404);
+        }
+
+        try {
+            $this->service->deleteTranslation($document, $locale);
+        } catch (\InvalidArgumentException $e) {
+            return response()->json(['message' => $e->getMessage()], 422);
+        }
+
+        return redirect()->route('documents.show', $document)
+            ->with('message', __('messages.documents.translation_deleted'));
+    }
+}

src/app/Livewire/DocumentEditor.php

@@ -2,30 +2,44 @@
 
 namespace App\Livewire;
 
+use App\Http\Middleware\SetLocale;
 use App\Models\Document;
 use App\Services\DocumentService;
-use Livewire\Component;
+use Illuminate\Support\Facades\App;
 use Illuminate\Support\Facades\Auth;
+use Livewire\Component;
 
 class DocumentEditor extends Component
 {
     public ?Document $document = null;
-    public $title = '';
-    public $content = '';
-    public $directory = '';
-    public $isEditMode = false;
+    public string $title = '';
+    public string $content = '';
+    public string $editingLocale = '';
+    public bool $isEditMode = false;
+    public bool $isNewLocale = false;
+    public array $availableLocales = [];
 
-    public function mount(?Document $document = null)
+    public function mount(?Document $document = null, ?string $locale = null)
     {
         if ($document) {
             $this->authorize('update', $document);
-
-            $this->document = $document;
-            $this->title = $document->title;
-            $this->content = $document->content;
-            $this->directory = $document->directory;
+            $this->document = $document->load('translations');
             $this->isEditMode = true;
+            $this->availableLocales = $document->availableLocales();
+            $this->editingLocale = $locale ?: ($document->default_locale ?? App::getLocale());
+
+            $translation = $document->translations->firstWhere('locale', $this->editingLocale);
+            if ($translation) {
+                $this->title = $translation->title;
+                $this->content = $translation->content;
+                $this->isNewLocale = false;
+            } else {
+                $this->title = '';
+                $this->content = '';
+                $this->isNewLocale = true;
+            }
         } else {
+            $this->editingLocale = App::getLocale();
             $titleParam = request()->query('title');
             if ($titleParam) {
                 $this->title = $titleParam;
@@ -35,53 +49,96 @@ public function mount(?Document $document = null)
 
     public function save(DocumentService $documentService)
     {
-        $this->validate([
+        $validated = $this->validate([
             'title' => 'required|string|max:255',
             'content' => 'required|string',
+            'editingLocale' => ['required', 'string', 'in:' . implode(',', array_keys(SetLocale::SUPPORTED_LOCALES))],
         ]);
 
         try {
             if ($this->isEditMode && $this->document) {
                 $this->authorize('update', $this->document);
 
-                $this->document = $documentService->updateDocument(
-                    $this->document,
-                    $this->title,
-                    $this->content,
-                    Auth::id()
-                );
+                if ($this->isNewLocale) {
+                    $documentService->addTranslation(
+                        $this->document,
+                        $this->editingLocale,
+                        $this->title,
+                        $this->content,
+                        Auth::id(),
+                    );
+                    $this->document->refresh()->load('translations');
+                } else {
+                    $this->document = $documentService->updateDocument(
+                        $this->document,
+                        $this->title,
+                        $this->content,
+                        Auth::id(),
+                        $this->editingLocale,
+                    );
+                }
 
-                session()->flash('message', 'Document updated successfully!');
+                session()->flash('message', __('messages.documents.update_success'));
                 return $this->redirect(route('documents.show', $this->document));
             } else {
                 $this->document = $documentService->createDocument(
                     $this->title,
                     $this->content,
                     Auth::id(),
-                    $this->directory ?: null
+                    $this->editingLocale,
                 );
-
-                session()->flash('message', 'Document created successfully!');
+                session()->flash('message', __('messages.documents.create_success'));
                 return $this->redirect(route('documents.show', $this->document));
             }
+        } catch (\InvalidArgumentException $e) {
+            session()->flash('error', $e->getMessage());
         } catch (\Exception $e) {
             session()->flash('error', 'Error saving document: ' . $e->getMessage());
         }
     }
 
+    public function deleteTranslation(DocumentService $documentService)
+    {
+        if (!$this->isEditMode || !$this->document || $this->isNewLocale) {
+            return;
+        }
+        $this->authorize('update', $this->document);
+
+        try {
+            $documentService->deleteTranslation($this->document, $this->editingLocale);
+            session()->flash('message', __('messages.documents.translation_deleted'));
+            return $this->redirect(route('documents.show', $this->document));
+        } catch (\InvalidArgumentException $e) {
+            session()->flash('error', $e->getMessage());
+        }
+    }
+
+    public function setAsDefault(DocumentService $documentService)
+    {
+        if (!$this->isEditMode || !$this->document) {
+            return;
+        }
+        $this->authorize('update', $this->document);
+
+        try {
+            $this->document = $documentService->setDefaultLocale($this->document, $this->editingLocale);
+            session()->flash('message', __('messages.documents.update_success'));
+            return $this->redirect(route('documents.show', $this->document));
+        } catch (\InvalidArgumentException $e) {
+            session()->flash('error', $e->getMessage());
+        }
+    }
+
     public function delete(DocumentService $documentService)
     {
         if (!$this->isEditMode || !$this->document) {
             return;
         }
-
         $this->authorize('delete', $this->document);
 
         try {
             $documentService->deleteDocument($this->document);
-            session()->flash('message', 'Document deleted successfully!');
-
-            // Try to redirect to home document, or root if not found
+            session()->flash('message', __('messages.documents.delete_success'));
             $homeDocument = Document::where('slug', 'home')->first();
             if ($homeDocument) {
                 return redirect()->route('documents.show', $homeDocument);
@@ -96,7 +153,9 @@ public function render()
     {
         return view('livewire.document-editor')
             ->layout('layouts.knowledge-base', [
-                'title' => $this->isEditMode ? 'Edit: ' . $this->title : 'New Document'
+                'title' => $this->isEditMode
+                    ? __('messages.documents.edit_document') . ': ' . $this->title
+                    : __('messages.documents.new_document'),
             ]);
     }
 }

src/app/Livewire/DocumentViewer.php

@@ -4,25 +4,32 @@
 
 use App\Models\Document;
 use App\Services\DocumentService;
-use Livewire\Component;
+use Illuminate\Support\Facades\App;
 use Illuminate\Support\Facades\Auth;
+use Livewire\Component;
 
 class DocumentViewer extends Component
 {
     public Document $document;
     public $backlinks = [];
-    public $renderedContent = '';
+    public string $renderedContent = '';
+    public string $viewLocale = '';
+    public bool $isFallback = false;
 
     public function mount(Document $document, DocumentService $documentService)
     {
-        $this->document = $document;
+        $this->document = $document->load('translations');
 
-        $this->renderedContent = $this->document->processLinks();
+        $current = App::getLocale();
+        $translation = $document->translationFor($current, fallback: true);
 
-        $this->backlinks = $documentService->getBacklinks($this->document);
+        $this->viewLocale = $translation?->locale ?? $document->default_locale;
+        $this->isFallback = ($current !== $this->viewLocale);
+        $this->renderedContent = $document->processLinks();
+        $this->backlinks = $documentService->getBacklinks($document);
 
         if (Auth::check()) {
-            $documentService->recordDocumentAccess($this->document, Auth::id());
+            $documentService->recordDocumentAccess($document, Auth::id());
         }
     }
 

src/app/Livewire/QuickSwitcher.php

@@ -4,65 +4,32 @@
 
 use App\Models\Document;
 use App\Services\DocumentService;
-use Livewire\Component;
 use Livewire\Attributes\Computed;
+use Livewire\Component;
 
 class QuickSwitcher extends Component
 {
-    public $search = '';
-    public $selectedIndex = 0;
+    public string $search = '';
+    public int $selectedIndex = 0;
 
     #[Computed]
     public function results()
     {
         if (empty($this->search)) {
-            return Document::select('id', 'title', 'slug', 'path', 'updated_at')
+            $documents = Document::with('translations')
                 ->orderBy('updated_at', 'desc')
                 ->limit(10)
-                ->get()
-                ->map(fn($doc) => [
-                    'id' => $doc->id,
-                    'title' => $doc->title,
-                    'slug' => $doc->slug,
-                    'directory' => dirname($doc->path),
-                ])
-                ->toArray();
+                ->get();
+        } else {
+            $documents = app(DocumentService::class)->search($this->search, 10);
         }
 
-        // FULLTEXT検索を使用（日本語対応）
-        $results = Document::select('id', 'title', 'slug', 'path', 'updated_at')
-            ->whereRaw('MATCH(title, content) AGAINST(? IN BOOLEAN MODE)', [$this->search])
-            ->orderBy('updated_at', 'desc')
-            ->limit(10)
-            ->get()
-            ->map(fn($doc) => [
-                'id' => $doc->id,
-                'title' => $doc->title,
-                'slug' => $doc->slug,
-                'directory' => dirname($doc->path),
-            ])
-            ->toArray();
-
-        // FULLTEXT検索で結果がない場合は LIKE 検索にフォールバック
-        if (empty($results)) {
-            $results = Document::select('id', 'title', 'slug', 'path', 'updated_at')
-                ->where(function($query) {
-                    $query->where('title', 'like', '%' . $this->search . '%')
-                          ->orWhere('content', 'like', '%' . $this->search . '%');
-                })
-                ->orderBy('updated_at', 'desc')
-                ->limit(10)
-                ->get()
-                ->map(fn($doc) => [
-                    'id' => $doc->id,
-                    'title' => $doc->title,
-                    'slug' => $doc->slug,
-                    'directory' => dirname($doc->path),
-                ])
-                ->toArray();
-        }
-
-        return $results;
+        return $documents->map(fn ($doc) => [
+            'id' => $doc->id,
+            'title' => $doc->title,
+            'slug' => $doc->slug,
+            'directory' => dirname($doc->path),
+        ])->values()->toArray();
     }
 
     public function updated($propertyName)
@@ -92,8 +59,6 @@ public function selectDocument()
         $results = $this->results;
         if (isset($results[$this->selectedIndex])) {
             $document = $results[$this->selectedIndex];
-
-            // slug が存在することを確認
             if (!empty($document['slug'])) {
                 return $this->redirect(route('documents.show', $document['slug']));
             }

src/app/Models/Document.php

@@ -3,64 +3,25 @@
 namespace App\Models;
 
 use App\Helpers\SlugHelper;
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
-use Illuminate\Database\Eloquent\SoftDeletes;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
 use Illuminate\Database\Eloquent\Relations\HasMany;
 use Illuminate\Database\Eloquent\Relations\HasManyThrough;
-use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Relations\HasOne;
+use Illuminate\Database\Eloquent\SoftDeletes;
+use Illuminate\Support\Facades\App;
 use Illuminate\Support\Facades\Storage;
-use Illuminate\Support\Str;
-use League\CommonMark\CommonMarkConverter;
-use League\CommonMark\Extension\CommonMark\Node\Inline\Link;
-use League\CommonMark\Extension\GithubFlavoredMarkdownExtension;
 
 class Document extends Model
 {
-    use SoftDeletes;
+    use HasFactory, SoftDeletes;
 
-    /**
-     * Get the route key for the model.
-     *
-     * @return string
-     */
-    public function getRouteKeyName(): string
-    {
-        return 'slug';
-    }
-
-    /**
-     * Retrieve the model for a bound value.
-     * Supports both slug and ID for backwards compatibility.
-     *
-     * @param  mixed  $value
-     * @param  string|null  $field
-     * @return \Illuminate\Database\Eloquent\Model|null
-     */
-    public function resolveRouteBinding($value, $field = null)
-    {
-        // First try to find by slug
-        $document = $this->where('slug', $value)->first();
-        
-        // If not found by slug, try by ID (for backwards compatibility)
-        if (!$document && is_numeric($value)) {
-            $document = $this->where('id', $value)->first();
-        }
-        
-        return $document;
-    }
-
-    /**
-     * The attributes that are mass assignable.
-     *
-     * @var list<string>
-     */
     protected $fillable = [
         'path',
-        'title',
         'slug',
-        'content',
-        'rendered_html',
+        'default_locale',
         'frontmatter',
         'file_size',
         'file_hash',
@@ -69,11 +30,6 @@ public function resolveRouteBinding($value, $field = null)
         'updated_by',
     ];
 
-    /**
-     * Get the attributes that should be cast.
-     *
-     * @return array<string, string>
-     */
     protected function casts(): array
     {
         return [
@@ -82,192 +38,64 @@ protected function casts(): array
         ];
     }
 
-    /**
-     * Frontmatterをパース（互換性のため残す）
-     *
-     * @param string $content
-     * @return array{frontmatter: array, content: string}
-     */
-    protected static function parseFrontmatter(string $content): array
+    public function getRouteKeyName(): string
     {
-        $frontmatter = [];
-        $bodyContent = $content;
+        return 'slug';
+    }
 
-        // Frontmatterの検出（--- で囲まれた部分）
-        if (preg_match('/^---\s*\n(.*?)\n---\s*\n(.*)/s', $content, $matches)) {
-            $frontmatterText = $matches[1];
-            $bodyContent = $matches[2];
+    public function resolveRouteBinding($value, $field = null)
+    {
+        $document = $this->where('slug', $value)->first();
 
-            // 簡易的なYAMLパース（key: value形式のみ）
-            $lines = explode("\n", $frontmatterText);
-            foreach ($lines as $line) {
-                if (preg_match('/^([^:]+):\s*(.*)$/', $line, $lineMatches)) {
-                    $frontmatter[trim($lineMatches[1])] = trim($lineMatches[2]);
-                }
-            }
+        if (!$document && is_numeric($value)) {
+            $document = $this->where('id', $value)->first();
         }
 
-        return [
-            'frontmatter' => $frontmatter,
-            'content' => trim($bodyContent),
-        ];
+        return $document;
     }
 
     /**
-     * Markdownをレンダリング
-     *
-     * @param string $markdown
-     * @return string
+     * Backward-compatible static delegate so existing callers and tests
+     * (e.g. MediaEmbedExtensionTest) keep working.
      */
     public static function renderMarkdown(string $markdown): string
     {
-        $converter = new CommonMarkConverter([
-            'html_input' => 'strip',
-            'allow_unsafe_links' => false,
-        ]);
-
-        $converter->getEnvironment()->addExtension(new GithubFlavoredMarkdownExtension());
-        $converter->getEnvironment()->addExtension(new \App\Markdown\MediaEmbedExtension());
-
-        return $converter->convert($markdown)->getContent();
+        return DocumentTranslation::renderMarkdown($markdown);
     }
 
-    /**
-     * [[wiki-link]]を抽出してリンクテーブルに同期
-     *
-     * @return void
-     */
-    public function syncLinks(): void
+    // ----- Relations -----
+
+    public function translations(): HasMany
     {
-        // 既存のリンクを削除
-        $this->outgoingLinks()->delete();
-
-        // [[wiki-link]]を抽出
-        preg_match_all('/\[\[([^\]]+)\]\]/', $this->content, $matches);
-
-        if (empty($matches[1])) {
-            return;
-        }
-
-        $position = 0;
-        foreach ($matches[1] as $linkTitle) {
-            $linkTitle = trim($linkTitle);
-
-            // リンク先のドキュメントを検索
-            $targetDocument = static::where('title', $linkTitle)
-                ->orWhere('slug', SlugHelper::generate($linkTitle))
-                ->first();
-
-            DocumentLink::create([
-                'source_document_id' => $this->id,
-                'target_document_id' => $targetDocument?->id,
-                'target_title' => $linkTitle,
-                'position' => $position++,
-            ]);
-        }
+        return $this->hasMany(DocumentTranslation::class);
     }
 
-    /**
-     * [[wiki-link]]をHTMLリンクに変換
-     *
-     * @return string
-     */
-    public function processLinks(): string
+    public function defaultTranslation(): HasOne
     {
-        return preg_replace_callback(
-            '/\[\[([^\]]+)\]\]/',
-            function ($matches) {
-                $linkTitle = trim($matches[1]);
-                $slug = SlugHelper::generate($linkTitle);
-
-                // リンク先のドキュメントを検索
-                $targetDocument = static::where('title', $linkTitle)
-                    ->orWhere('slug', $slug)
-                    ->first();
-
-                if ($targetDocument) {
-                    return '<a href="' . route('documents.show', $targetDocument->slug) . '" class="wiki-link">' . e($linkTitle) . '</a>';
-                } else {
-                    return '<a href="' . route('documents.create') . '?title=' . urlencode($linkTitle) . '" class="wiki-link wiki-link-new">' . e($linkTitle) . '</a>';
-                }
-            },
-            $this->rendered_html
-        );
+        return $this->hasOne(DocumentTranslation::class)
+            ->whereColumn('locale', 'documents.default_locale');
     }
 
-    /**
-     * 全文検索スコープ
-     *
-     * @param Builder $query
-     * @param string $searchTerm
-     * @return Builder
-     */
-    public function scopeSearch(Builder $query, string $searchTerm): Builder
-    {
-        return $query->whereRaw(
-            'MATCH(title, content) AGAINST(? IN BOOLEAN MODE)',
-            [$searchTerm]
-        );
-    }
-
-    /**
-     * ディレクトリ内検索スコープ
-     *
-     * @param Builder $query
-     * @param string $directory
-     * @return Builder
-     */
-    public function scopeInDirectory(Builder $query, string $directory): Builder
-    {
-        $directory = rtrim($directory, '/') . '/';
-        return $query->where('path', 'like', $directory . '%');
-    }
-
-    /**
-     * 作成者リレーション
-     *
-     * @return BelongsTo
-     */
     public function creator(): BelongsTo
     {
         return $this->belongsTo(User::class, 'created_by');
     }
 
-    /**
-     * 更新者リレーション
-     *
-     * @return BelongsTo
-     */
     public function updater(): BelongsTo
     {
         return $this->belongsTo(User::class, 'updated_by');
     }
 
-    /**
-     * 発リンク（このドキュメントから他へのリンク）
-     *
-     * @return HasMany
-     */
     public function outgoingLinks(): HasMany
     {
         return $this->hasMany(DocumentLink::class, 'source_document_id');
     }
 
-    /**
-     * 被リンク（他のドキュメントからこのドキュメントへのリンク）
-     *
-     * @return HasMany
-     */
     public function incomingLinks(): HasMany
     {
         return $this->hasMany(DocumentLink::class, 'target_document_id');
     }
 
-    /**
-     * このドキュメントを最近閲覧したユーザー
-     *
-     * @return HasManyThrough
-     */
     public function recentByUsers(): HasManyThrough
     {
         return $this->hasManyThrough(
@@ -280,48 +108,142 @@ public function recentByUsers(): HasManyThrough
         );
     }
 
+    // ----- Translation helpers -----
+
+    public function translationFor(string $locale, bool $fallback = true): ?DocumentTranslation
+    {
+        $translation = $this->translations->firstWhere('locale', $locale);
+
+        if (!$translation && $fallback) {
+            $translation = $this->translations->firstWhere('locale', $this->default_locale);
+        }
+
+        return $translation;
+    }
+
+    public function isFallback(string $requestedLocale): bool
+    {
+        return $this->translations->firstWhere('locale', $requestedLocale) === null;
+    }
+
     /**
-     * ディレクトリパスを取得
-     *
-     * @return string
+     * @return array<int, string>
      */
+    public function availableLocales(): array
+    {
+        return $this->translations->pluck('locale')->all();
+    }
+
+    // ----- Accessors (current-locale → fallback) -----
+
+    public function getTitleAttribute(): string
+    {
+        return $this->translationFor(App::getLocale())?->title ?? '';
+    }
+
+    public function getContentAttribute(): string
+    {
+        return $this->translationFor(App::getLocale())?->content ?? '';
+    }
+
+    public function getRenderedHtmlAttribute(): ?string
+    {
+        return $this->translationFor(App::getLocale())?->rendered_html;
+    }
+
+    // ----- Path helpers -----
+
     public function getDirectoryAttribute(): string
     {
         return dirname($this->path);
     }
 
-    /**
-     * ファイル名を取得
-     *
-     * @return string
-     */
     public function getFilenameAttribute(): string
     {
         return basename($this->path);
     }
 
-    /**
-     * 絶対パスを取得
-     *
-     * @return string
-     */
     public function getAbsolutePathAttribute(): string
     {
         return Storage::disk('markdown')->path($this->path);
     }
 
-    /**
-     * タイトルセット時にslugも自動生成
-     *
-     * @param string $value
-     * @return void
-     */
-    public function setTitleAttribute(string $value): void
-    {
-        $this->attributes['title'] = $value;
+    // ----- Search scope (delegates to translations) -----
 
-        if (empty($this->attributes['slug'])) {
-            $this->attributes['slug'] = SlugHelper::generate($value);
+    public function scopeSearch(Builder $query, string $term): Builder
+    {
+        return $query->whereHas('translations', function (Builder $q) use ($term) {
+            DocumentTranslation::scopeSearch($q, $term);
+        });
+    }
+
+    public function scopeInDirectory(Builder $query, string $directory): Builder
+    {
+        $directory = rtrim($directory, '/') . '/';
+        return $query->where('path', 'like', $directory . '%');
+    }
+
+    /**
+     * Extract [[wiki-links]] from the default-locale translation's content
+     * and persist them via DocumentLink.
+     */
+    public function syncLinks(): void
+    {
+        $this->outgoingLinks()->delete();
+
+        $translation = $this->translationFor($this->default_locale, fallback: false);
+        if (!$translation || !$translation->content) {
+            return;
+        }
+
+        preg_match_all('/\[\[([^\]]+)\]\]/', $translation->content, $matches);
+        if (empty($matches[1])) {
+            return;
+        }
+
+        $resolver = new \App\Services\WikiLinkResolver();
+        $position = 0;
+        foreach ($matches[1] as $linkTitle) {
+            $linkTitle = trim($linkTitle);
+            $target = $resolver->resolve($linkTitle, $this->default_locale);
+
+            DocumentLink::create([
+                'source_document_id' => $this->id,
+                'target_document_id' => $target?->id,
+                'target_title' => $linkTitle,
+                'position' => $position++,
+            ]);
         }
     }
+
+    /**
+     * Convert [[wiki-links]] in the current-locale rendered_html to anchor tags.
+     * Link labels stay in the original language; the destination document is
+     * resolved against the current locale (with fallback).
+     */
+    public function processLinks(): string
+    {
+        $html = $this->rendered_html ?? '';
+        if ($html === '') {
+            return '';
+        }
+
+        $resolver = new \App\Services\WikiLinkResolver();
+        $currentLocale = App::getLocale();
+
+        return preg_replace_callback(
+            '/\[\[([^\]]+)\]\]/',
+            function ($matches) use ($resolver, $currentLocale) {
+                $linkText = trim($matches[1]);
+                $target = $resolver->resolve($linkText, $currentLocale);
+
+                if ($target) {
+                    return '<a href="' . route('documents.show', $target->slug) . '" class="wiki-link">' . e($linkText) . '</a>';
+                }
+
+                return '<a href="' . route('documents.create') . '?title=' . urlencode($linkText) . '" class="wiki-link wiki-link-new">' . e($linkText) . '</a>';
+            },
+            $html
+        );
+    }
 }

src/app/Models/DocumentTranslation.php

@@ -0,0 +1,72 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use League\CommonMark\CommonMarkConverter;
+use League\CommonMark\Extension\GithubFlavoredMarkdownExtension;
+
+class DocumentTranslation extends Model
+{
+    use HasFactory;
+
+    protected $fillable = [
+        'document_id',
+        'locale',
+        'title',
+        'content',
+        'rendered_html',
+        'created_by',
+        'updated_by',
+    ];
+
+    public function document(): BelongsTo
+    {
+        return $this->belongsTo(Document::class);
+    }
+
+    public function creator(): BelongsTo
+    {
+        return $this->belongsTo(User::class, 'created_by');
+    }
+
+    public function updater(): BelongsTo
+    {
+        return $this->belongsTo(User::class, 'updated_by');
+    }
+
+    /**
+     * Full-text search scope. Falls back to LIKE on non-MySQL drivers
+     * (notably SQLite in tests, which lacks FULLTEXT).
+     */
+    public function scopeSearch(Builder $query, string $term): Builder
+    {
+        if ($query->getConnection()->getDriverName() === 'mysql') {
+            return $query->whereRaw(
+                'MATCH(title, content) AGAINST(? IN BOOLEAN MODE)',
+                [$term]
+            );
+        }
+
+        return $query->where(function (Builder $q) use ($term) {
+            $like = '%' . $term . '%';
+            $q->where('title', 'like', $like)->orWhere('content', 'like', $like);
+        });
+    }
+
+    public static function renderMarkdown(string $markdown): string
+    {
+        $converter = new CommonMarkConverter([
+            'html_input' => 'strip',
+            'allow_unsafe_links' => false,
+        ]);
+
+        $converter->getEnvironment()->addExtension(new GithubFlavoredMarkdownExtension());
+        $converter->getEnvironment()->addExtension(new \App\Markdown\MediaEmbedExtension());
+
+        return $converter->convert($markdown)->getContent();
+    }
+}

src/app/Services/DocumentService.php

@@ -2,143 +2,185 @@
 
 namespace App\Services;
 
-use App\Models\Document;
-use App\Models\RecentDocument;
 use App\Helpers\SlugHelper;
-use Illuminate\Support\Facades\Storage;
+use App\Models\Document;
+use App\Models\DocumentTranslation;
+use App\Models\RecentDocument;
+use Illuminate\Support\Facades\App;
 use Illuminate\Support\Facades\DB;
-use Illuminate\Support\Str;
 
 class DocumentService
 {
-
-    /**
-     * 新しいドキュメントを作成
-     *
-     * @param string $title
-     * @param string $content
-     * @param int|null $userId
-     * @param string|null $directory (deprecated - path is now auto-generated from title)
-     * @return Document
-     */
     public function createDocument(
         string $title,
         string $content,
         ?int $userId = null,
-        ?string $directory = null
+        ?string $locale = null,
     ): Document {
-        // タイトルからパスとスラッグを自動生成
-        // 例: "Laravel/Livewire/Components" → path="Laravel/Livewire/Components.md", slug="components"
+        $locale = $locale ?: App::getLocale();
         [$path, $slug] = $this->generatePathAndSlug($title);
 
-        // ドキュメントをDBに作成
-        $document = Document::create([
-            'path' => $path,
-            'title' => $title,
-            'slug' => $slug,
-            'content' => $content,
-            'rendered_html' => Document::renderMarkdown($content),
-            'created_by' => $userId,
-            'updated_by' => $userId,
-        ]);
+        return DB::transaction(function () use ($title, $content, $userId, $locale, $path, $slug) {
+            $document = Document::create([
+                'path' => $path,
+                'slug' => $slug,
+                'default_locale' => $locale,
+                'created_by' => $userId,
+                'updated_by' => $userId,
+            ]);
 
-        // リンクを同期
-        $document->syncLinks();
+            DocumentTranslation::create([
+                'document_id' => $document->id,
+                'locale' => $locale,
+                'title' => $title,
+                'content' => $content,
+                'rendered_html' => DocumentTranslation::renderMarkdown($content),
+                'created_by' => $userId,
+                'updated_by' => $userId,
+            ]);
 
-        return $document;
+            $document->load('translations');
+            $document->syncLinks();
+
+            return $document;
+        });
     }
 
-    /**
-     * ドキュメントを更新
-     *
-     * @param Document $document
-     * @param string $title
-     * @param string $content
-     * @param int|null $userId
-     * @return Document
-     */
     public function updateDocument(
         Document $document,
         string $title,
         string $content,
-        ?int $userId = null
+        ?int $userId = null,
+        ?string $locale = null,
     ): Document {
-        // タイトルが変更された場合はパスとスラッグを再生成
-        if ($document->title !== $title) {
-            [$path, $slug] = $this->generatePathAndSlug($title, $document->id);
-            $document->path = $path;
-            $document->slug = $slug;
-        }
+        $locale = $locale ?: App::getLocale();
 
-        $document->title = $title;
-        $document->content = $content;
-        $document->rendered_html = Document::renderMarkdown($content);
-        $document->updated_by = $userId;
+        return DB::transaction(function () use ($document, $title, $content, $userId, $locale) {
+            $translation = $document->translations()->firstOrNew(['locale' => $locale]);
+            $translation->title = $title;
+            $translation->content = $content;
+            $translation->rendered_html = DocumentTranslation::renderMarkdown($content);
+            $translation->updated_by = $userId;
+            if (!$translation->exists) {
+                $translation->created_by = $userId;
+            }
+            $translation->save();
 
-        // DBに保存
-        $document->save();
+            $document->updated_by = $userId;
 
-        // リンクを再同期
-        $document->syncLinks();
+            // Path/slug regenerate only when editing the default-locale translation
+            if ($locale === $document->default_locale) {
+                [$path, $slug] = $this->generatePathAndSlug($title, $document->id);
+                $document->path = $path;
+                $document->slug = $slug;
+            }
 
-        return $document;
+            $document->save();
+            $document->load('translations');
+            $document->syncLinks();
+
+            return $document;
+        });
+    }
+
+    public function addTranslation(
+        Document $document,
+        string $locale,
+        string $title,
+        string $content,
+        ?int $userId = null,
+    ): DocumentTranslation {
+        if ($document->translations()->where('locale', $locale)->exists()) {
+            throw new \InvalidArgumentException("Translation for locale '$locale' already exists");
+        }
+
+        return DocumentTranslation::create([
+            'document_id' => $document->id,
+            'locale' => $locale,
+            'title' => $title,
+            'content' => $content,
+            'rendered_html' => DocumentTranslation::renderMarkdown($content),
+            'created_by' => $userId,
+            'updated_by' => $userId,
+        ]);
+    }
+
+    public function deleteTranslation(Document $document, string $locale): void
+    {
+        if ($locale === $document->default_locale) {
+            throw new \InvalidArgumentException("Cannot delete default-locale translation '$locale'");
+        }
+        $document->translations()->where('locale', $locale)->delete();
+    }
+
+    public function setDefaultLocale(Document $document, string $locale): Document
+    {
+        $translation = $document->translations()->where('locale', $locale)->first();
+        if (!$translation) {
+            throw new \InvalidArgumentException("Cannot set default to '$locale': translation does not exist");
+        }
+
+        return DB::transaction(function () use ($document, $locale, $translation) {
+            $document->default_locale = $locale;
+            [$path, $slug] = $this->generatePathAndSlug($translation->title, $document->id);
+            $document->path = $path;
+            $document->slug = $slug;
+            $document->save();
+
+            return $document->fresh('translations');
+        });
     }
 
-    /**
-     * ドキュメントを削除
-     *
-     * @param Document $document
-     * @return bool
-     */
     public function deleteDocument(Document $document): bool
     {
-        // DBから削除（ソフトデリート）
         return $document->delete();
     }
 
     /**
-     * 全文検索
-     *
-     * @param string $query
-     * @param int $limit
-     * @return \Illuminate\Database\Eloquent\Collection
+     * Locale-agnostic full-text search; returns distinct documents.
      */
     public function search(string $query, int $limit = 20)
     {
-        return Document::search($query)
-            ->limit($limit)
-            ->get();
+        $documentIds = DocumentTranslation::query()
+            ->search($query)
+            ->limit($limit * 5) // overscan to allow distinct collapse
+            ->pluck('document_id')
+            ->unique()
+            ->values()
+            ->take($limit);
+
+        if ($documentIds->isEmpty()) {
+            return Document::query()->whereRaw('1 = 0')->get();
+        }
+
+        return Document::with('translations')
+            ->whereIn('id', $documentIds)
+            ->get()
+            ->sortBy(fn ($d) => $documentIds->search($d->id))
+            ->values();
+    }
+
+    public function findByTitle(string $title, ?string $locale = null): ?Document
+    {
+        return (new WikiLinkResolver())->resolve($title, $locale ?: App::getLocale());
     }
 
-    /**
-     * ディレクトリツリーを生成
-     *
-     * @return array
-     */
     public function getDirectoryTree(): array
     {
-        $documents = Document::orderBy('path')->get();
+        $documents = Document::with('translations')->orderBy('path')->get();
 
         $tree = [];
-
         foreach ($documents as $document) {
             $parts = explode('/', $document->path);
             $current = &$tree;
-
             foreach ($parts as $index => $part) {
                 $isFile = ($index === count($parts) - 1);
-
                 if ($isFile) {
-                    // ファイル
-                    if (!isset($current['_files'])) {
-                        $current['_files'] = [];
-                    }
                     $current['_files'][] = [
                         'name' => $part,
                         'document' => $document,
                     ];
                 } else {
-                    // ディレクトリ
                     if (!isset($current[$part])) {
                         $current[$part] = [];
                     }
@@ -146,67 +188,28 @@ public function getDirectoryTree(): array
                 }
             }
         }
-
         return $tree;
     }
 
-    /**
-     * ユーザーの最近閲覧したドキュメントを取得
-     *
-     * @param int $userId
-     * @param int $limit
-     * @return \Illuminate\Database\Eloquent\Collection
-     */
     public function getRecentDocuments(int $userId, int $limit = 10)
     {
         return RecentDocument::getRecentForUser($userId, $limit);
     }
 
-    /**
-     * ドキュメント閲覧を記録
-     *
-     * @param Document $document
-     * @param int $userId
-     * @return void
-     */
     public function recordDocumentAccess(Document $document, int $userId): void
     {
         RecentDocument::recordAccess($userId, $document->id);
     }
 
-    /**
-     * 指定タイトルのドキュメントを検索
-     *
-     * @param string $title
-     * @return Document|null
-     */
-    public function findByTitle(string $title): ?Document
-    {
-        return Document::where('title', $title)
-            ->orWhere('slug', SlugHelper::generate($title))
-            ->first();
-    }
-
-    /**
-     * 被リンク（バックリンク）を取得
-     *
-     * @param Document $document
-     * @return \Illuminate\Database\Eloquent\Collection
-     */
     public function getBacklinks(Document $document)
     {
         return $document->incomingLinks()
-            ->with('sourceDocument')
+            ->with('sourceDocument.translations')
             ->get()
             ->pluck('sourceDocument')
             ->filter();
     }
 
-    /**
-     * 壊れたリンク（未作成ページへのリンク）を取得
-     *
-     * @return \Illuminate\Database\Eloquent\Collection
-     */
     public function getBrokenLinks()
     {
         return DB::table('document_links')
@@ -217,39 +220,13 @@ public function getBrokenLinks()
             ->get();
     }
 
-    /**
-     * タイトルからパスとスラッグを生成
-     * タイトルに含まれる / をディレクトリ区切りとして扱う
-     *
-     * 例: "Laravel/Livewire/Components"
-     *     → path = "Laravel/Livewire/Components.md"
-     *     → slug = "components" (最後のコンポーネントから生成)
-     *
-     * @param string $title
-     * @param int|null $excludeDocumentId 更新時に除外するドキュメントID
-     * @return array [path, slug]
-     */
     private function generatePathAndSlug(string $title, ?int $excludeDocumentId = null): array
     {
-        // タイトルをそのままパスとして使用（.md拡張子を追加）
         $basePath = $title . '.md';
-
-        // 最後のパスコンポーネント（スラッシュで区切られた最後の部分）からスラッグを生成
-        $lastComponent = basename($title);
-        $baseSlug = SlugHelper::generate($lastComponent);
-
-        // ユニークなパスとスラッグを生成
+        $baseSlug = SlugHelper::generate(basename($title));
         return $this->ensureUniquePath($basePath, $baseSlug, $excludeDocumentId);
     }
 
-    /**
-     * パスとスラッグがユニークになるように調整
-     *
-     * @param string $basePath
-     * @param string $baseSlug
-     * @param int|null $excludeDocumentId
-     * @return array [path, slug]
-     */
     private function ensureUniquePath(string $basePath, string $baseSlug, ?int $excludeDocumentId = null): array
     {
         $path = $basePath;
@@ -261,46 +238,17 @@ private function ensureUniquePath(string $basePath, string $baseSlug, ?int $excl
                 ->where(function ($q) use ($path, $slug) {
                     $q->where('path', $path)->orWhere('slug', $slug);
                 });
-
             if ($excludeDocumentId) {
                 $query->where('id', '!=', $excludeDocumentId);
             }
-
             if (!$query->exists()) {
                 break;
             }
-
             $counter++;
-            // パス: "title.md" → "title-2.md"
             $path = preg_replace('/\.md$/', "-{$counter}.md", $basePath);
-            // スラッグ: "title" → "title-2"
             $slug = $baseSlug . '-' . $counter;
         }
 
         return [$path, $slug];
     }
-
-    /**
-     * 初期ドキュメントを作成
-     *
-     * @return void
-     */
-    public function createInitialDocuments(): void
-    {
-        // ホームページ
-        $this->createDocument(
-            'Home',
-            "# Welcome to Knowledge Base\n\nThis is your personal knowledge base powered by Markdown.\n\n## Getting Started\n\n- Create new documents using [[wiki-links]]\n- Use Ctrl+K for quick switching\n- Full-text search is available\n\n## Example Links\n\n- [[Getting Started]]\n- [[Documentation]]\n- [[Notes]]",
-            null,
-            null
-        );
-
-        // Getting Startedページ
-        $this->createDocument(
-            'Getting Started',
-            "# Getting Started\n\nLearn how to use this knowledge base.\n\n## Creating Documents\n\nClick on any [[wiki-link]] to create a new document.\n\n## Editing\n\nClick the edit button to modify content.\n\nBack to [[Home]]",
-            null,
-            null
-        );
-    }
 }

src/app/Services/WikiLinkResolver.php

@@ -0,0 +1,64 @@
+<?php
+
+namespace App\Services;
+
+use App\Helpers\SlugHelper;
+use App\Models\Document;
+use App\Models\DocumentTranslation;
+
+class WikiLinkResolver
+{
+    /**
+     * Resolve [[wiki-link]] text to a Document, preferring the current locale.
+     *
+     * Resolution order:
+     *   1. translations WHERE locale = $currentLocale          AND title = $linkText
+     *   2. translations WHERE locale = document.default_locale AND title = $linkText
+     *   3. translations WHERE                                       title = $linkText (lowest document_id wins)
+     *   4. documents    WHERE slug = SlugHelper::generate($linkText)
+     *   5. null
+     */
+    public function resolve(string $linkText, string $currentLocale): ?Document
+    {
+        $linkText = trim($linkText);
+
+        // 1. Current-locale exact title match
+        $byCurrent = DocumentTranslation::where('locale', $currentLocale)
+            ->where('title', $linkText)
+            ->orderBy('document_id')
+            ->first();
+        if ($byCurrent) {
+            return $byCurrent->document;
+        }
+
+        // 2. Document's default-locale title match
+        $byDefault = DocumentTranslation::query()
+            ->join('documents', 'documents.id', '=', 'document_translations.document_id')
+            ->whereColumn('document_translations.locale', 'documents.default_locale')
+            ->where('document_translations.title', $linkText)
+            ->orderBy('document_translations.document_id')
+            ->select('document_translations.*')
+            ->first();
+        if ($byDefault) {
+            return $byDefault->document;
+        }
+
+        // 3. Any-locale title match (lowest document_id wins)
+        $byAny = DocumentTranslation::where('title', $linkText)
+            ->orderBy('document_id')
+            ->first();
+        if ($byAny) {
+            return $byAny->document;
+        }
+
+        // 4. Slug match (legacy)
+        $slug = SlugHelper::generate($linkText);
+        $bySlug = Document::where('slug', $slug)->first();
+        if ($bySlug) {
+            return $bySlug;
+        }
+
+        // 5. Nothing
+        return null;
+    }
+}

src/database/factories/DocumentFactory.php

@@ -0,0 +1,65 @@
+<?php
+
+namespace Database\Factories;
+
+use App\Helpers\SlugHelper;
+use App\Models\Document;
+use App\Models\DocumentTranslation;
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+/**
+ * @extends Factory<Document>
+ */
+class DocumentFactory extends Factory
+{
+    protected $model = Document::class;
+
+    public function definition(): array
+    {
+        $title = rtrim(fake()->unique()->words(3, true), '.');
+
+        return [
+            'path' => $title . '.md',
+            'slug' => SlugHelper::generate($title),
+            'default_locale' => 'en',
+            'file_size' => 0,
+            'file_hash' => str_repeat('0', 64),
+            'file_modified_at' => now(),
+        ];
+    }
+
+    /**
+     * After creating, attach a translation in the document's default_locale
+     * (skipped if a translation was already created via state, or if the
+     * caller used withoutTranslations()).
+     */
+    public function configure(): static
+    {
+        return $this->afterCreating(function (Document $document) {
+            if ($document->translations()->count() === 0) {
+                DocumentTranslation::factory()->create([
+                    'document_id' => $document->id,
+                    'locale' => $document->default_locale,
+                ]);
+            }
+        });
+    }
+
+    /**
+     * Override the default_locale (auto-translation will be created in this locale).
+     */
+    public function defaultLocale(string $locale): static
+    {
+        return $this->state(['default_locale' => $locale]);
+    }
+
+    /**
+     * Suppress automatic translation creation. Uses Laravel's built-in
+     * withoutAfterCreating() to clear callbacks rather than appending a no-op
+     * (afterCreating appends, so a no-op closure does NOT override the configure() callback).
+     */
+    public function withoutTranslations(): static
+    {
+        return $this->withoutAfterCreating();
+    }
+}

src/database/factories/DocumentTranslationFactory.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace Database\Factories;
+
+use App\Models\Document;
+use App\Models\DocumentTranslation;
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+/**
+ * @extends Factory<DocumentTranslation>
+ */
+class DocumentTranslationFactory extends Factory
+{
+    protected $model = DocumentTranslation::class;
+
+    public function definition(): array
+    {
+        $title = fake()->sentence(3);
+        $content = fake()->paragraphs(3, true);
+
+        return [
+            'document_id' => Document::factory()->withoutTranslations(),
+            'locale' => 'en',
+            'title' => $title,
+            'content' => $content,
+            'rendered_html' => '<p>' . e($content) . '</p>',
+        ];
+    }
+}

src/database/migrations/2024_11_28_100001_create_documents_table.php

@@ -2,6 +2,7 @@
 
 use Illuminate\Database\Migrations\Migration;
 use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\DB;
 use Illuminate\Support\Facades\Schema;
 
 return new class extends Migration
@@ -27,7 +28,9 @@ public function up(): void
 
         // FULLTEXT検索インデックス（MySQL 5.7以降）
         // ngramトークナイザーは日本語対応に必要だが、設定が必要
-        DB::statement('ALTER TABLE documents ADD FULLTEXT INDEX documents_search_index (title, content) WITH PARSER ngram');
+        if (DB::connection()->getDriverName() === 'mysql') {
+            DB::statement('ALTER TABLE documents ADD FULLTEXT INDEX documents_search_index (title, content) WITH PARSER ngram');
+        }
 
         // 検索パフォーマンス向上用インデックス
         Schema::table('documents', function (Blueprint $table) {

src/database/migrations/2026_05_10_000001_create_document_translations_and_migrate.php

@@ -0,0 +1,115 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        // 1. Add default_locale to documents
+        Schema::table('documents', function (Blueprint $table) {
+            $table->string('default_locale', 10)
+                ->default(config('app.locale', 'en'))
+                ->after('slug');
+        });
+
+        // 2. Create document_translations
+        Schema::create('document_translations', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('document_id')->constrained('documents')->cascadeOnDelete();
+            $table->string('locale', 10);
+            $table->string('title');
+            $table->text('content');
+            $table->text('rendered_html')->nullable();
+            $table->foreignId('created_by')->nullable()->constrained('users')->nullOnDelete();
+            $table->foreignId('updated_by')->nullable()->constrained('users')->nullOnDelete();
+            $table->timestamps();
+
+            $table->unique(['document_id', 'locale']);
+            $table->index(['locale', 'title']);
+        });
+
+        if (DB::connection()->getDriverName() === 'mysql') {
+            DB::statement('ALTER TABLE document_translations ADD FULLTEXT INDEX document_translations_search_index (title, content) WITH PARSER ngram');
+        }
+
+        // 3. Migrate existing data
+        // Note: step 4 (ALTER TABLE … DROP INDEX) must remain OUTSIDE this
+        // transaction because MySQL's ALTER TABLE causes an implicit commit.
+        $defaultLocale = config('app.locale', 'en');
+        $now = now();
+        DB::transaction(function () use ($defaultLocale, $now) {
+            DB::table('documents')->orderBy('id')->chunkById(500, function ($rows) use ($defaultLocale, $now) {
+                foreach ($rows as $row) {
+                    DB::table('document_translations')->insert([
+                        'document_id' => $row->id,
+                        'locale' => $defaultLocale,
+                        'title' => $row->title ?? '',
+                        'content' => $row->content ?? '',
+                        'rendered_html' => $row->rendered_html,
+                        'created_by' => $row->created_by ?? null,
+                        'updated_by' => $row->updated_by ?? null,
+                        'created_at' => $row->created_at ?? $now,
+                        'updated_at' => $row->updated_at ?? $now,
+                    ]);
+                    DB::table('documents')->where('id', $row->id)->update(['default_locale' => $defaultLocale]);
+                }
+            });
+        });
+
+        // 4. Drop the old FULLTEXT index on documents (MySQL only)
+        if (DB::connection()->getDriverName() === 'mysql') {
+            DB::statement('ALTER TABLE documents DROP INDEX documents_search_index');
+        }
+
+        // 5. Drop translatable columns from documents
+        // Drop the title index first (SQLite requires this before dropping the column)
+        Schema::table('documents', function (Blueprint $table) {
+            $table->dropIndex(['title']);
+            $table->dropColumn(['title', 'content', 'rendered_html']);
+        });
+    }
+
+    public function down(): void
+    {
+        // IRREVERSIBLE for non-default-locale translations: only the row matching
+        // each document's default_locale is restored to the legacy columns; any
+        // other-locale translations are dropped along with document_translations.
+
+        // Re-add columns (with the title index that up() expects to drop)
+        Schema::table('documents', function (Blueprint $table) {
+            $table->string('title')->nullable()->index()->after('default_locale');
+            $table->text('content')->nullable()->after('title');
+            $table->text('rendered_html')->nullable()->after('content');
+        });
+
+        // Restore data from default_locale translation
+        $rows = DB::table('document_translations as t')
+            ->join('documents as d', 'd.id', '=', 't.document_id')
+            ->whereColumn('t.locale', 'd.default_locale')
+            ->select('t.document_id', 't.title', 't.content', 't.rendered_html')
+            ->get();
+
+        foreach ($rows as $row) {
+            DB::table('documents')->where('id', $row->document_id)->update([
+                'title' => $row->title,
+                'content' => $row->content,
+                'rendered_html' => $row->rendered_html,
+            ]);
+        }
+
+        // Restore FULLTEXT on documents (MySQL only)
+        if (DB::connection()->getDriverName() === 'mysql') {
+            DB::statement('ALTER TABLE documents ADD FULLTEXT INDEX documents_search_index (title, content) WITH PARSER ngram');
+        }
+
+        Schema::dropIfExists('document_translations');
+
+        Schema::table('documents', function (Blueprint $table) {
+            $table->dropColumn('default_locale');
+        });
+    }
+};

src/database/seeders/DocumentSeeder.php

@@ -2,7 +2,6 @@
 
 namespace Database\Seeders;
 
-use App\Models\Document;
 use Illuminate\Database\Seeder;
 
 class DocumentSeeder extends Seeder
@@ -12,43 +11,23 @@ class DocumentSeeder extends Seeder
      */
     public function run(): void
     {
-        // 既存のドキュメントがある場合はスキップ
-        if (Document::count() > 0) {
+        if (\App\Models\Document::count() > 0) {
             $this->command->info('Documents already exist. Skipping...');
             return;
         }
 
-        $documents = [
-            [
-                'title' => 'Home',
-                'path' => 'Home.md',
-                'slug' => 'home',
-                'content' => $this->getHomeContent(),
-            ],
-            [
-                'title' => 'Getting Started',
-                'path' => 'Getting Started.md',
-                'slug' => 'getting-started',
-                'content' => $this->getGettingStartedContent(),
-            ],
-            [
-                'title' => 'Markdown Guide',
-                'path' => 'Markdown Guide.md',
-                'slug' => 'markdown-guide',
-                'content' => $this->getMarkdownGuideContent(),
-            ],
+        $service = app(\App\Services\DocumentService::class);
+        $defaultLocale = config('app.locale', 'en');
+
+        $docs = [
+            ['title' => 'Home', 'content' => $this->getHomeContent()],
+            ['title' => 'Getting Started', 'content' => $this->getGettingStartedContent()],
+            ['title' => 'Markdown Guide', 'content' => $this->getMarkdownGuideContent()],
         ];
 
-        foreach ($documents as $doc) {
-            Document::create([
-                'title' => $doc['title'],
-                'path' => $doc['path'],
-                'slug' => $doc['slug'],
-                'content' => $doc['content'],
-                'rendered_html' => Document::renderMarkdown($doc['content']),
-            ]);
-
-            $this->command->info("Created: {$doc['title']}");
+        foreach ($docs as $d) {
+            $service->createDocument($d['title'], $d['content'], null, $defaultLocale);
+            $this->command->info("Created: {$d['title']}");
         }
 
         $this->command->info('Initial documents created successfully!');

src/lang/de/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Inhalt',
         'content_placeholder' => 'Schreiben Sie hier Ihren Markdown...',
         'saving' => 'Speichern...',
+        'fallback_notice' => 'Eine Übersetzung dieses Artikels in der von Ihnen gewählten Sprache ist nicht verfügbar. Die Originalsprachversion wird angezeigt.',
+        'add_translation' => 'Übersetzung hinzufügen',
+        'translation_added' => 'Übersetzung hinzugefügt.',
+        'translation_deleted' => 'Übersetzung gelöscht.',
+        'set_as_default' => 'Als Standard festlegen',
+        'delete_translation' => 'Übersetzung löschen',
+        'delete_translation_blocked' => 'Die Übersetzung der Standardsprache kann nicht gelöscht werden.',
+        'translation_tabs_label' => 'Sprachen',
     ],
 
     // Quick Switcher
@@ -123,6 +131,25 @@
         'back_to_home' => 'Zurück zur Startseite',
     ],
 
+    'locale_names' => [
+        'en' => 'Englisch',
+        'ja' => 'Japanisch',
+        'zh-CN' => 'Chinesisch (vereinfacht)',
+        'zh-TW' => 'Chinesisch (traditionell)',
+        'ko' => 'Koreanisch',
+        'hi' => 'Hindi',
+        'vi' => 'Vietnamesisch',
+        'tr' => 'Türkisch',
+        'de' => 'Deutsch',
+        'fr' => 'Französisch',
+        'es' => 'Spanisch',
+        'pt-BR' => 'Portugiesisch (Brasilien)',
+        'ru' => 'Russisch',
+        'uk' => 'Ukrainisch',
+        'it' => 'Italienisch',
+        'pl' => 'Polnisch',
+    ],
+
     // Profile
     'profile' => [
         'title' => 'Profil',

src/lang/en/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Content',
         'content_placeholder' => 'Write your markdown here...',
         'saving' => 'Saving...',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        'fallback_notice' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'set_as_default' => 'Set as default',
+        'delete_translation' => 'Delete translation',
+        'delete_translation_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -123,6 +131,25 @@
         'back_to_home' => 'Back to Home',
     ],
 
+    'locale_names' => [
+        'en' => 'English',
+        'ja' => 'Japanese',
+        'zh-CN' => 'Simplified Chinese',
+        'zh-TW' => 'Traditional Chinese',
+        'ko' => 'Korean',
+        'hi' => 'Hindi',
+        'vi' => 'Vietnamese',
+        'tr' => 'Turkish',
+        'de' => 'German',
+        'fr' => 'French',
+        'es' => 'Spanish',
+        'pt-BR' => 'Portuguese (Brazil)',
+        'ru' => 'Russian',
+        'uk' => 'Ukrainian',
+        'it' => 'Italian',
+        'pl' => 'Polish',
+    ],
+
     // Profile
     'profile' => [
         'title' => 'Profile',

src/lang/es/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Contenido',
         'content_placeholder' => 'Escriba su markdown aquí...',
         'saving' => 'Guardando...',
+        'fallback_notice' => 'Este artículo no está traducido al idioma seleccionado. Se muestra la versión en el idioma original.',
+        'add_translation' => 'Añadir traducción',
+        'translation_added' => 'Traducción añadida.',
+        'translation_deleted' => 'Traducción eliminada.',
+        'set_as_default' => 'Establecer como predeterminado',
+        'delete_translation' => 'Eliminar traducción',
+        'delete_translation_blocked' => 'No se puede eliminar la traducción del idioma predeterminado.',
+        'translation_tabs_label' => 'Idiomas',
     ],
 
     // Quick Switcher
@@ -123,6 +131,25 @@
         'back_to_home' => 'Volver al inicio',
     ],
 
+    'locale_names' => [
+        'en' => 'Inglés',
+        'ja' => 'Japonés',
+        'zh-CN' => 'Chino (simplificado)',
+        'zh-TW' => 'Chino (tradicional)',
+        'ko' => 'Coreano',
+        'hi' => 'Hindi',
+        'vi' => 'Vietnamita',
+        'tr' => 'Turco',
+        'de' => 'Alemán',
+        'fr' => 'Francés',
+        'es' => 'Español',
+        'pt-BR' => 'Portugués (Brasil)',
+        'ru' => 'Ruso',
+        'uk' => 'Ucraniano',
+        'it' => 'Italiano',
+        'pl' => 'Polaco',
+    ],
+
     // Profile
     'profile' => [
         'title' => 'Perfil',

src/lang/fr/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Contenu',
         'content_placeholder' => 'Écrivez votre markdown ici...',
         'saving' => 'Enregistrement...',
+        'fallback_notice' => 'Cet article n\'est pas traduit dans la langue sélectionnée. La version dans la langue d\'origine est affichée.',
+        'add_translation' => 'Ajouter une traduction',
+        'translation_added' => 'Traduction ajoutée.',
+        'translation_deleted' => 'Traduction supprimée.',
+        'set_as_default' => 'Définir par défaut',
+        'delete_translation' => 'Supprimer la traduction',
+        'delete_translation_blocked' => 'La traduction de la langue par défaut ne peut pas être supprimée.',
+        'translation_tabs_label' => 'Langues',
     ],
 
     // Quick Switcher
@@ -123,6 +131,25 @@
         'back_to_home' => 'Retour à l\'accueil',
     ],
 
+    'locale_names' => [
+        'en' => 'Anglais',
+        'ja' => 'Japonais',
+        'zh-CN' => 'Chinois (simplifié)',
+        'zh-TW' => 'Chinois (traditionnel)',
+        'ko' => 'Coréen',
+        'hi' => 'Hindi',
+        'vi' => 'Vietnamien',
+        'tr' => 'Turc',
+        'de' => 'Allemand',
+        'fr' => 'Français',
+        'es' => 'Espagnol',
+        'pt-BR' => 'Portugais (Brésil)',
+        'ru' => 'Russe',
+        'uk' => 'Ukrainien',
+        'it' => 'Italien',
+        'pl' => 'Polonais',
+    ],
+
     // Profile
     'profile' => [
         'title' => 'Profil',

src/lang/hi/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'सामग्री',
         'content_placeholder' => 'यहां अपना मार्कडाउन लिखें...',
         'saving' => 'सहेजा जा रहा है...',
+        'fallback_notice' => 'इस लेख का आपकी चुनी गई भाषा में अनुवाद उपलब्ध नहीं है। मूल भाषा का संस्करण दिखाया जा रहा है।',
+        'add_translation' => 'अनुवाद जोड़ें',
+        'translation_added' => 'अनुवाद जोड़ा गया।',
+        'translation_deleted' => 'अनुवाद हटाया गया।',
+        'set_as_default' => 'डिफ़ॉल्ट के रूप में सेट करें',
+        'delete_translation' => 'अनुवाद हटाएं',
+        'delete_translation_blocked' => 'डिफ़ॉल्ट भाषा का अनुवाद हटाया नहीं जा सकता।',
+        'translation_tabs_label' => 'भाषाएँ',
     ],
 
     // Quick Switcher
@@ -124,6 +132,25 @@
         'back_to_home' => 'होम पर वापस जाएं',
     ],
 
+    'locale_names' => [
+        'en' => 'अंग्रेज़ी',
+        'ja' => 'जापानी',
+        'zh-CN' => 'चीनी (सरलीकृत)',
+        'zh-TW' => 'चीनी (पारंपरिक)',
+        'ko' => 'कोरियाई',
+        'hi' => 'हिन्दी',
+        'vi' => 'वियतनामी',
+        'tr' => 'तुर्की',
+        'de' => 'जर्मन',
+        'fr' => 'फ़्रेंच',
+        'es' => 'स्पेनिश',
+        'pt-BR' => 'पुर्तगाली (ब्राज़ील)',
+        'ru' => 'रूसी',
+        'uk' => 'यूक्रेनी',
+        'it' => 'इतालवी',
+        'pl' => 'पोलिश',
+    ],
+
     // Profile
     'profile' => [
         'title' => 'प्रोफ़ाइल',

src/lang/it/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Contenuto',
         'content_placeholder' => 'Scrivi il tuo markdown qui...',
         'saving' => 'Salvataggio...',
+        'fallback_notice' => 'Questo articolo non è tradotto nella lingua selezionata. Viene mostrata la versione nella lingua originale.',
+        'add_translation' => 'Aggiungi traduzione',
+        'translation_added' => 'Traduzione aggiunta.',
+        'translation_deleted' => 'Traduzione eliminata.',
+        'set_as_default' => 'Imposta come predefinita',
+        'delete_translation' => 'Elimina traduzione',
+        'delete_translation_blocked' => 'La traduzione della lingua predefinita non può essere eliminata.',
+        'translation_tabs_label' => 'Lingue',
     ],
 
     // Quick Switcher
@@ -124,6 +132,25 @@
         'back_to_home' => 'Torna alla Home',
     ],
 
+    'locale_names' => [
+        'en' => 'Inglese',
+        'ja' => 'Giapponese',
+        'zh-CN' => 'Cinese (semplificato)',
+        'zh-TW' => 'Cinese (tradizionale)',
+        'ko' => 'Coreano',
+        'hi' => 'Hindi',
+        'vi' => 'Vietnamita',
+        'tr' => 'Turco',
+        'de' => 'Tedesco',
+        'fr' => 'Francese',
+        'es' => 'Spagnolo',
+        'pt-BR' => 'Portoghese (Brasile)',
+        'ru' => 'Russo',
+        'uk' => 'Ucraino',
+        'it' => 'Italiano',
+        'pl' => 'Polacco',
+    ],
+
     // Profile
     'profile' => [
         'title' => 'Profilo',

src/lang/ja/messages.php

@@ -39,6 +39,14 @@
         'content_label' => '本文',
         'content_placeholder' => 'Markdownで記述してください...',
         'saving' => '保存中...',
+        'translation_added' => '翻訳を追加しました。',
+        'translation_deleted' => '翻訳を削除しました。',
+        'fallback_notice' => 'この記事には選択した言語の翻訳がありません。元の言語版を表示しています。',
+        'add_translation' => '翻訳を追加',
+        'set_as_default' => 'デフォルトに設定',
+        'delete_translation' => '翻訳を削除',
+        'delete_translation_blocked' => 'デフォルト言語の翻訳は削除できません。',
+        'translation_tabs_label' => '言語',
     ],
 
     // Quick Switcher
@@ -123,6 +131,14 @@
         'back_to_home' => 'ホームに戻る',
     ],
 
+    'locale_names' => [
+        'en' => '英語', 'ja' => '日本語',
+        'zh-CN' => '簡体字中国語', 'zh-TW' => '繁体字中国語',
+        'ko' => '韓国語', 'hi' => 'ヒンディー語', 'vi' => 'ベトナム語', 'tr' => 'トルコ語',
+        'de' => 'ドイツ語', 'fr' => 'フランス語', 'es' => 'スペイン語', 'pt-BR' => 'ポルトガル語(ブラジル)',
+        'ru' => 'ロシア語', 'uk' => 'ウクライナ語', 'it' => 'イタリア語', 'pl' => 'ポーランド語',
+    ],
+
     // Profile
     'profile' => [
         'title' => 'プロフィール',

src/lang/ko/messages.php

@@ -39,6 +39,14 @@
         'content_label' => '내용',
         'content_placeholder' => '여기에 마크다운을 작성하세요...',
         'saving' => '저장 중...',
+        'fallback_notice' => '이 문서에는 선택한 언어의 번역이 없습니다. 원본 언어 버전을 표시합니다.',
+        'add_translation' => '번역 추가',
+        'translation_added' => '번역이 추가되었습니다.',
+        'translation_deleted' => '번역이 삭제되었습니다.',
+        'set_as_default' => '기본값으로 설정',
+        'delete_translation' => '번역 삭제',
+        'delete_translation_blocked' => '기본 언어의 번역은 삭제할 수 없습니다.',
+        'translation_tabs_label' => '언어',
     ],
 
     // Quick Switcher
@@ -123,6 +131,25 @@
         'back_to_home' => '홈으로 돌아가기',
     ],
 
+    'locale_names' => [
+        'en' => '영어',
+        'ja' => '일본어',
+        'zh-CN' => '중국어 간체',
+        'zh-TW' => '중국어 번체',
+        'ko' => '한국어',
+        'hi' => '힌디어',
+        'vi' => '베트남어',
+        'tr' => '터키어',
+        'de' => '독일어',
+        'fr' => '프랑스어',
+        'es' => '스페인어',
+        'pt-BR' => '포르투갈어 (브라질)',
+        'ru' => '러시아어',
+        'uk' => '우크라이나어',
+        'it' => '이탈리아어',
+        'pl' => '폴란드어',
+    ],
+
     // Profile
     'profile' => [
         'title' => '프로필',

src/lang/pl/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Treść',
         'content_placeholder' => 'Napisz swój markdown tutaj...',
         'saving' => 'Zapisywanie...',
+        'fallback_notice' => 'Ten artykuł nie został przetłumaczony na wybrany język. Wyświetlana jest wersja w języku oryginału.',
+        'add_translation' => 'Dodaj tłumaczenie',
+        'translation_added' => 'Tłumaczenie dodane.',
+        'translation_deleted' => 'Tłumaczenie usunięte.',
+        'set_as_default' => 'Ustaw jako domyślny',
+        'delete_translation' => 'Usuń tłumaczenie',
+        'delete_translation_blocked' => 'Nie można usunąć tłumaczenia w języku domyślnym.',
+        'translation_tabs_label' => 'Języki',
     ],
 
     // Quick Switcher
@@ -124,6 +132,25 @@
         'back_to_home' => 'Wróć do strony głównej',
     ],
 
+    'locale_names' => [
+        'en' => 'Angielski',
+        'ja' => 'Japoński',
+        'zh-CN' => 'Chiński (uproszczony)',
+        'zh-TW' => 'Chiński (tradycyjny)',
+        'ko' => 'Koreański',
+        'hi' => 'Hindi',
+        'vi' => 'Wietnamski',
+        'tr' => 'Turecki',
+        'de' => 'Niemiecki',
+        'fr' => 'Francuski',
+        'es' => 'Hiszpański',
+        'pt-BR' => 'Portugalski (Brazylia)',
+        'ru' => 'Rosyjski',
+        'uk' => 'Ukraiński',
+        'it' => 'Włoski',
+        'pl' => 'Polski',
+    ],
+
     // Profile
     'profile' => [
         'title' => 'Profil',

src/lang/pt-BR/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Conteúdo',
         'content_placeholder' => 'Escreva seu markdown aqui...',
         'saving' => 'Salvando...',
+        'fallback_notice' => 'Este artigo não possui tradução para o idioma selecionado. Exibindo a versão no idioma original.',
+        'add_translation' => 'Adicionar tradução',
+        'translation_added' => 'Tradução adicionada.',
+        'translation_deleted' => 'Tradução excluída.',
+        'set_as_default' => 'Definir como padrão',
+        'delete_translation' => 'Excluir tradução',
+        'delete_translation_blocked' => 'A tradução do idioma padrão não pode ser excluída.',
+        'translation_tabs_label' => 'Idiomas',
     ],
 
     // Quick Switcher
@@ -124,6 +132,25 @@
         'back_to_home' => 'Voltar para Início',
     ],
 
+    'locale_names' => [
+        'en' => 'Inglês',
+        'ja' => 'Japonês',
+        'zh-CN' => 'Chinês (simplificado)',
+        'zh-TW' => 'Chinês (tradicional)',
+        'ko' => 'Coreano',
+        'hi' => 'Híndi',
+        'vi' => 'Vietnamita',
+        'tr' => 'Turco',
+        'de' => 'Alemão',
+        'fr' => 'Francês',
+        'es' => 'Espanhol',
+        'pt-BR' => 'Português (Brasil)',
+        'ru' => 'Russo',
+        'uk' => 'Ucraniano',
+        'it' => 'Italiano',
+        'pl' => 'Polonês',
+    ],
+
     // Profile
     'profile' => [
         'title' => 'Perfil',

src/lang/ru/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Содержимое',
         'content_placeholder' => 'Напишите здесь ваш markdown...',
         'saving' => 'Сохранение...',
+        'fallback_notice' => 'Эта статья не переведена на выбранный язык. Отображается версия на языке оригинала.',
+        'add_translation' => 'Добавить перевод',
+        'translation_added' => 'Перевод добавлен.',
+        'translation_deleted' => 'Перевод удалён.',
+        'set_as_default' => 'Установить по умолчанию',
+        'delete_translation' => 'Удалить перевод',
+        'delete_translation_blocked' => 'Перевод языка по умолчанию нельзя удалить.',
+        'translation_tabs_label' => 'Языки',
     ],
 
     // Quick Switcher
@@ -124,6 +132,25 @@
         'back_to_home' => 'Вернуться на главную',
     ],
 
+    'locale_names' => [
+        'en' => 'Английский',
+        'ja' => 'Японский',
+        'zh-CN' => 'Китайский (упрощённый)',
+        'zh-TW' => 'Китайский (традиционный)',
+        'ko' => 'Корейский',
+        'hi' => 'Хинди',
+        'vi' => 'Вьетнамский',
+        'tr' => 'Турецкий',
+        'de' => 'Немецкий',
+        'fr' => 'Французский',
+        'es' => 'Испанский',
+        'pt-BR' => 'Португальский (Бразилия)',
+        'ru' => 'Русский',
+        'uk' => 'Украинский',
+        'it' => 'Итальянский',
+        'pl' => 'Польский',
+    ],
+
     // Profile
     'profile' => [
         'title' => 'Профиль',

src/lang/tr/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'İçerik',
         'content_placeholder' => 'Markdown\'ınızı buraya yazın...',
         'saving' => 'Kaydediliyor...',
+        'fallback_notice' => 'Bu makalenin seçtiğiniz dile çevirisi mevcut değil. Orijinal dil sürümü gösteriliyor.',
+        'add_translation' => 'Çeviri ekle',
+        'translation_added' => 'Çeviri eklendi.',
+        'translation_deleted' => 'Çeviri silindi.',
+        'set_as_default' => 'Varsayılan olarak ayarla',
+        'delete_translation' => 'Çeviriyi sil',
+        'delete_translation_blocked' => 'Varsayılan dilin çevirisi silinemez.',
+        'translation_tabs_label' => 'Diller',
     ],
 
     // Quick Switcher
@@ -124,6 +132,25 @@
         'back_to_home' => 'Ana Sayfaya Dön',
     ],
 
+    'locale_names' => [
+        'en' => 'İngilizce',
+        'ja' => 'Japonca',
+        'zh-CN' => 'Basitleştirilmiş Çince',
+        'zh-TW' => 'Geleneksel Çince',
+        'ko' => 'Korece',
+        'hi' => 'Hintçe',
+        'vi' => 'Vietnamca',
+        'tr' => 'Türkçe',
+        'de' => 'Almanca',
+        'fr' => 'Fransızca',
+        'es' => 'İspanyolca',
+        'pt-BR' => 'Portekizce (Brezilya)',
+        'ru' => 'Rusça',
+        'uk' => 'Ukraynaca',
+        'it' => 'İtalyanca',
+        'pl' => 'Lehçe',
+    ],
+
     // Profile
     'profile' => [
         'title' => 'Profil',

src/lang/uk/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Вміст',
         'content_placeholder' => 'Напишіть тут ваш markdown...',
         'saving' => 'Збереження...',
+        'fallback_notice' => 'Цю статтю не перекладено вибраною мовою. Відображається версія мовою оригіналу.',
+        'add_translation' => 'Додати переклад',
+        'translation_added' => 'Переклад додано.',
+        'translation_deleted' => 'Переклад видалено.',
+        'set_as_default' => 'Встановити за замовчуванням',
+        'delete_translation' => 'Видалити переклад',
+        'delete_translation_blocked' => 'Переклад мови за замовчуванням не можна видалити.',
+        'translation_tabs_label' => 'Мови',
     ],
 
     // Quick Switcher
@@ -124,6 +132,25 @@
         'back_to_home' => 'Повернутися на головну',
     ],
 
+    'locale_names' => [
+        'en' => 'Англійська',
+        'ja' => 'Японська',
+        'zh-CN' => 'Китайська (спрощена)',
+        'zh-TW' => 'Китайська (традиційна)',
+        'ko' => 'Корейська',
+        'hi' => 'Гінді',
+        'vi' => 'В\'єтнамська',
+        'tr' => 'Турецька',
+        'de' => 'Німецька',
+        'fr' => 'Французька',
+        'es' => 'Іспанська',
+        'pt-BR' => 'Португальська (Бразилія)',
+        'ru' => 'Російська',
+        'uk' => 'Українська',
+        'it' => 'Італійська',
+        'pl' => 'Польська',
+    ],
+
     // Profile
     'profile' => [
         'title' => 'Профіль',

src/lang/vi/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Nội dung',
         'content_placeholder' => 'Viết markdown của bạn ở đây...',
         'saving' => 'Đang lưu...',
+        'fallback_notice' => 'Bài viết này không có bản dịch sang ngôn ngữ bạn đã chọn. Đang hiển thị phiên bản ngôn ngữ gốc.',
+        'add_translation' => 'Thêm bản dịch',
+        'translation_added' => 'Đã thêm bản dịch.',
+        'translation_deleted' => 'Đã xoá bản dịch.',
+        'set_as_default' => 'Đặt làm mặc định',
+        'delete_translation' => 'Xoá bản dịch',
+        'delete_translation_blocked' => 'Không thể xoá bản dịch của ngôn ngữ mặc định.',
+        'translation_tabs_label' => 'Ngôn ngữ',
     ],
 
     // Quick Switcher
@@ -124,6 +132,25 @@
         'back_to_home' => 'Quay lại trang chủ',
     ],
 
+    'locale_names' => [
+        'en' => 'Tiếng Anh',
+        'ja' => 'Tiếng Nhật',
+        'zh-CN' => 'Tiếng Trung (Giản thể)',
+        'zh-TW' => 'Tiếng Trung (Phồn thể)',
+        'ko' => 'Tiếng Hàn',
+        'hi' => 'Tiếng Hindi',
+        'vi' => 'Tiếng Việt',
+        'tr' => 'Tiếng Thổ Nhĩ Kỳ',
+        'de' => 'Tiếng Đức',
+        'fr' => 'Tiếng Pháp',
+        'es' => 'Tiếng Tây Ban Nha',
+        'pt-BR' => 'Tiếng Bồ Đào Nha (Brasil)',
+        'ru' => 'Tiếng Nga',
+        'uk' => 'Tiếng Ukraine',
+        'it' => 'Tiếng Ý',
+        'pl' => 'Tiếng Ba Lan',
+    ],
+
     // Profile
     'profile' => [
         'title' => 'Hồ sơ',

src/lang/zh-CN/messages.php

@@ -39,6 +39,14 @@
         'content_label' => '内容',
         'content_placeholder' => '在此输入Markdown内容...',
         'saving' => '保存中...',
+        'fallback_notice' => '此文章没有您所选语言的翻译。正在显示原语言版本。',
+        'add_translation' => '添加翻译',
+        'translation_added' => '翻译已添加。',
+        'translation_deleted' => '翻译已删除。',
+        'set_as_default' => '设为默认',
+        'delete_translation' => '删除翻译',
+        'delete_translation_blocked' => '无法删除默认语言的翻译。',
+        'translation_tabs_label' => '语言',
     ],
 
     // Quick Switcher
@@ -123,6 +131,25 @@
         'back_to_home' => '返回首页',
     ],
 
+    'locale_names' => [
+        'en' => '英语',
+        'ja' => '日语',
+        'zh-CN' => '简体中文',
+        'zh-TW' => '繁体中文',
+        'ko' => '韩语',
+        'hi' => '印地语',
+        'vi' => '越南语',
+        'tr' => '土耳其语',
+        'de' => '德语',
+        'fr' => '法语',
+        'es' => '西班牙语',
+        'pt-BR' => '葡萄牙语（巴西）',
+        'ru' => '俄语',
+        'uk' => '乌克兰语',
+        'it' => '意大利语',
+        'pl' => '波兰语',
+    ],
+
     // Profile
     'profile' => [
         'title' => '个人资料',

src/lang/zh-TW/messages.php

@@ -39,6 +39,14 @@
         'content_label' => '內容',
         'content_placeholder' => '在此輸入Markdown內容...',
         'saving' => '儲存中...',
+        'fallback_notice' => '此文章沒有您所選語言的翻譯。正在顯示原語言版本。',
+        'add_translation' => '新增翻譯',
+        'translation_added' => '翻譯已新增。',
+        'translation_deleted' => '翻譯已刪除。',
+        'set_as_default' => '設為預設',
+        'delete_translation' => '刪除翻譯',
+        'delete_translation_blocked' => '無法刪除預設語言的翻譯。',
+        'translation_tabs_label' => '語言',
     ],
 
     // Quick Switcher
@@ -123,6 +131,25 @@
         'back_to_home' => '返回首頁',
     ],
 
+    'locale_names' => [
+        'en' => '英語',
+        'ja' => '日語',
+        'zh-CN' => '簡體中文',
+        'zh-TW' => '繁體中文',
+        'ko' => '韓語',
+        'hi' => '印地語',
+        'vi' => '越南語',
+        'tr' => '土耳其語',
+        'de' => '德語',
+        'fr' => '法語',
+        'es' => '西班牙語',
+        'pt-BR' => '葡萄牙語（巴西）',
+        'ru' => '俄語',
+        'uk' => '烏克蘭語',
+        'it' => '義大利語',
+        'pl' => '波蘭語',
+    ],
+
     // Profile
     'profile' => [
         'title' => '個人資料',

src/resources/views/livewire/document-editor.blade.php

@@ -56,6 +56,65 @@ class="inline-flex items-center justify-center px-3 sm:px-4 py-2 bg-indigo-600 b
         </div>
     </div>
 
+    @if($isEditMode && $document)
+        <div class="mb-4 border-b border-gray-200" role="tablist" aria-label="{{ __('messages.documents.translation_tabs_label') }}">
+            <nav class="-mb-px flex flex-wrap gap-x-2">
+                @php $allLocales = \App\Http\Middleware\SetLocale::SUPPORTED_LOCALES; @endphp
+                @foreach($availableLocales as $loc)
+                    @php $isActive = ($loc === $editingLocale); @endphp
+                    <a href="{{ route('documents.translations.edit', ['document' => $document, 'locale' => $loc]) }}"
+                       class="px-3 py-2 text-sm font-medium border-b-2 {{ $isActive ? 'border-indigo-500 text-indigo-600' : 'border-transparent text-gray-500 hover:text-gray-700 hover:border-gray-300' }}">
+                        {{ __('messages.locale_names.' . $loc) }}
+                        @if($loc === $document->default_locale)
+                            <span class="ml-1 text-xs text-gray-400">★</span>
+                        @endif
+                    </a>
+                @endforeach
+
+                @if($isNewLocale && $editingLocale)
+                    <span class="px-3 py-2 text-sm font-medium border-b-2 border-indigo-500 text-indigo-600">
+                        {{ __('messages.locale_names.' . $editingLocale) }}
+                        <span class="ml-1 text-xs text-gray-400">({{ __('messages.documents.new_document') }})</span>
+                    </span>
+                @endif
+
+                @php $missingLocales = array_diff(array_keys($allLocales), $availableLocales, $isNewLocale ? [$editingLocale] : []); @endphp
+                @if(!empty($missingLocales))
+                    <div x-data="{ open: false }" class="relative">
+                        <button type="button" @click="open = !open"
+                                class="px-3 py-2 text-sm font-medium border-b-2 border-transparent text-gray-500 hover:text-gray-700 hover:border-gray-300">
+                            + {{ __('messages.documents.add_translation') }}
+                        </button>
+                        <div x-show="open" @click.outside="open = false" x-cloak
+                             class="absolute right-0 z-10 mt-2 w-48 max-h-64 overflow-y-auto bg-white border border-gray-200 rounded-md shadow-lg">
+                            @foreach($missingLocales as $loc)
+                                <a href="{{ route('documents.translations.edit', ['document' => $document, 'locale' => $loc]) }}"
+                                   class="block px-3 py-2 text-sm text-gray-700 hover:bg-gray-50">
+                                    {{ $allLocales[$loc] }}
+                                </a>
+                            @endforeach
+                        </div>
+                    </div>
+                @endif
+            </nav>
+
+            @if($editingLocale !== $document->default_locale && !$isNewLocale)
+                <div class="mt-2 flex gap-2">
+                    <button wire:click="setAsDefault" type="button"
+                            class="px-2 py-1 text-xs text-indigo-600 border border-indigo-300 rounded hover:bg-indigo-50">
+                        {{ __('messages.documents.set_as_default') }}
+                    </button>
+                    <button wire:click="deleteTranslation"
+                            wire:confirm="{{ __('messages.documents.delete_confirm') }}"
+                            type="button"
+                            class="px-2 py-1 text-xs text-red-600 border border-red-300 rounded hover:bg-red-50">
+                        {{ __('messages.documents.delete_translation') }}
+                    </button>
+                </div>
+            @endif
+        </div>
+    @endif
+
     <!-- Form -->
     <form wire:submit.prevent="save" class="space-y-6">
         <!-- Title -->

src/resources/views/livewire/document-viewer.blade.php

@@ -1,4 +1,20 @@
 <div class="max-w-4xl mx-auto p-4 sm:p-6 lg:p-8">
+    @if($isFallback)
+        <div class="mb-4 p-4 bg-amber-50 border border-amber-300 rounded-md flex flex-col sm:flex-row sm:items-center sm:justify-between gap-3">
+            <p class="text-sm text-amber-800">
+                {{ __('messages.documents.fallback_notice', ['locale' => __('messages.locale_names.' . $viewLocale)]) }}
+            </p>
+            @auth
+                @can('update', $document)
+                    <a href="{{ route('documents.translations.edit', ['document' => $document, 'locale' => app()->getLocale()]) }}"
+                       class="inline-flex items-center justify-center px-3 py-2 bg-amber-600 text-white text-sm font-medium rounded-md hover:bg-amber-700">
+                        {{ __('messages.documents.add_translation') }}
+                    </a>
+                @endcan
+            @endauth
+        </div>
+    @endif
+
     <!-- Document Header -->
     <div class="mb-6 sm:mb-8">
         <div class="flex flex-col sm:flex-row sm:items-start sm:justify-between gap-4 mb-4">

src/routes/web.php

@@ -47,6 +47,15 @@
         Route::get('/{document}/edit', DocumentEditor::class)
             ->middleware('can:update,document')
             ->name('edit');
+        Route::post('/{document}/translations', [\App\Http\Controllers\DocumentTranslationController::class, 'store'])
+            ->middleware('can:update,document')
+            ->name('translations.store');
+        Route::delete('/{document}/translations/{locale}', [\App\Http\Controllers\DocumentTranslationController::class, 'destroy'])
+            ->middleware('can:update,document')
+            ->name('translations.destroy');
+        Route::get('/{document}/translations/{locale}/edit', \App\Livewire\DocumentEditor::class)
+            ->middleware('can:update,document')
+            ->name('translations.edit');
     });
 
     // 公開ルート（動的ルートは最後に）

src/tests/Feature/DocumentI18nTest.php

@@ -0,0 +1,130 @@
+<?php
+
+namespace Tests\Feature;
+
+use App\Models\Document;
+use App\Models\DocumentTranslation;
+use App\Models\User;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\App;
+use Tests\TestCase;
+
+class DocumentI18nTest extends TestCase
+{
+    use RefreshDatabase;
+
+    public function test_viewer_shows_current_locale_translation(): void
+    {
+        $doc = Document::factory()->create(['default_locale' => 'en', 'slug' => 'hello']);
+        $doc->translations()->where('locale', 'en')->update(['title' => 'Hello', 'content' => 'Hi', 'rendered_html' => '<p>Hi</p>']);
+        DocumentTranslation::factory()->create([
+            'document_id' => $doc->id,
+            'locale' => 'ja',
+            'title' => 'こんにちは',
+            'content' => 'やあ',
+            'rendered_html' => '<p>やあ</p>',
+        ]);
+
+        session()->put('locale', 'ja');
+        $response = $this->get(route('documents.show', $doc));
+
+        $response->assertOk();
+        $response->assertSee('こんにちは');
+        $response->assertSee('やあ', false);
+    }
+
+    public function test_viewer_falls_back_with_banner_when_locale_missing(): void
+    {
+        $doc = Document::factory()->create(['default_locale' => 'en', 'slug' => 'fb']);
+        $doc->translations()->where('locale', 'en')->update(['title' => 'Hello', 'content' => 'Hi', 'rendered_html' => '<p>Hi</p>']);
+
+        session()->put('locale', 'ja');
+        $response = $this->get(route('documents.show', $doc));
+
+        $response->assertOk();
+        $response->assertSee('Hello'); // fallback content
+        // banner present (use the JA translation key value)
+        $response->assertSeeText(__('messages.documents.fallback_notice', [], 'ja'));
+    }
+
+    public function test_no_banner_when_translation_exists(): void
+    {
+        $doc = Document::factory()->create(['default_locale' => 'en', 'slug' => 'nb']);
+        $doc->translations()->where('locale', 'en')->update(['title' => 'Hello', 'content' => 'Hi', 'rendered_html' => '<p>Hi</p>']);
+        DocumentTranslation::factory()->create([
+            'document_id' => $doc->id,
+            'locale' => 'ja',
+            'title' => 'こんにちは',
+            'content' => 'やあ',
+            'rendered_html' => '<p>やあ</p>',
+        ]);
+
+        session()->put('locale', 'ja');
+        $response = $this->get(route('documents.show', $doc));
+
+        $response->assertOk();
+        $response->assertDontSeeText(__('messages.documents.fallback_notice', [], 'ja'));
+    }
+
+    public function test_editor_loads_existing_translation_for_locale(): void
+    {
+        $owner = \App\Models\User::factory()->create();
+        $doc = Document::factory()->create(['default_locale' => 'en', 'created_by' => $owner->id, 'slug' => 'editor']);
+        $doc->translations()->where('locale', 'en')->update(['title' => 'Hello', 'content' => 'EN body']);
+        DocumentTranslation::factory()->create([
+            'document_id' => $doc->id,
+            'locale' => 'ja',
+            'title' => 'こんにちは',
+            'content' => 'JA body',
+        ]);
+
+        $response = $this->actingAs($owner)->get(route('documents.translations.edit', [
+            'document' => $doc,
+            'locale' => 'ja',
+        ]));
+
+        $response->assertOk();
+        $response->assertSee('こんにちは');
+        $response->assertSee('JA body');
+    }
+
+    public function test_editor_for_missing_locale_shows_empty_form_with_new_locale_state(): void
+    {
+        $owner = \App\Models\User::factory()->create();
+        $doc = Document::factory()->create(['default_locale' => 'en', 'created_by' => $owner->id, 'slug' => 'editor2']);
+
+        $response = $this->actingAs($owner)->get(route('documents.translations.edit', [
+            'document' => $doc,
+            'locale' => 'ja',
+        ]));
+
+        $response->assertOk();
+        // The blade should render a tab marked active for ja with empty inputs
+        $response->assertSeeText(__('messages.locale_names.ja', [], 'en'));
+    }
+
+    public function test_quick_switcher_finds_documents_by_any_locale_title(): void
+    {
+        $doc = Document::factory()->create(['default_locale' => 'en', 'slug' => 'qs']);
+        $doc->translations()->where('locale', 'en')->update(['title' => 'Getting Started', 'content' => 'EN body']);
+        DocumentTranslation::factory()->create([
+            'document_id' => $doc->id,
+            'locale' => 'ja',
+            'title' => 'はじめに',
+            'content' => '本文',
+        ]);
+
+        $component = \Livewire\Livewire::test(\App\Livewire\QuickSwitcher::class)
+            ->set('search', 'はじめに');
+
+        $results = $component->get('results');
+        $this->assertCount(1, $results);
+        $this->assertSame($doc->id, $results[0]['id']);
+
+        $component2 = \Livewire\Livewire::test(\App\Livewire\QuickSwitcher::class)
+            ->set('search', 'Getting');
+        $results2 = $component2->get('results');
+        $this->assertCount(1, $results2);
+        $this->assertSame($doc->id, $results2[0]['id']);
+    }
+}

src/tests/Feature/DocumentMigrationTest.php

@@ -0,0 +1,114 @@
+<?php
+
+namespace Tests\Feature;
+
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+use Tests\TestCase;
+
+class DocumentMigrationTest extends TestCase
+{
+    use RefreshDatabase;
+
+    public function test_documents_table_has_default_locale_after_migration(): void
+    {
+        $this->assertTrue(Schema::hasColumn('documents', 'default_locale'));
+    }
+
+    public function test_documents_table_no_longer_has_translatable_columns(): void
+    {
+        $this->assertFalse(Schema::hasColumn('documents', 'title'));
+        $this->assertFalse(Schema::hasColumn('documents', 'content'));
+        $this->assertFalse(Schema::hasColumn('documents', 'rendered_html'));
+    }
+
+    public function test_document_translations_table_exists_with_required_columns(): void
+    {
+        $this->assertTrue(Schema::hasTable('document_translations'));
+
+        foreach (['document_id', 'locale', 'title', 'content', 'rendered_html', 'created_by', 'updated_by', 'created_at', 'updated_at'] as $col) {
+            $this->assertTrue(
+                Schema::hasColumn('document_translations', $col),
+                "document_translations missing column: $col"
+            );
+        }
+    }
+
+    public function test_document_translations_unique_document_locale(): void
+    {
+        DB::table('documents')->insert([
+            'path' => 'A.md',
+            'slug' => 'a',
+            'default_locale' => 'en',
+            'file_size' => 0,
+            'file_hash' => str_repeat('0', 64),
+            'file_modified_at' => now(),
+            'created_at' => now(),
+            'updated_at' => now(),
+        ]);
+        $docId = DB::table('documents')->where('slug', 'a')->value('id');
+
+        DB::table('document_translations')->insert([
+            'document_id' => $docId,
+            'locale' => 'en',
+            'title' => 'A',
+            'content' => '...',
+            'rendered_html' => '<p>...</p>',
+            'created_at' => now(),
+            'updated_at' => now(),
+        ]);
+
+        $this->expectException(\Illuminate\Database\QueryException::class);
+
+        DB::table('document_translations')->insert([
+            'document_id' => $docId,
+            'locale' => 'en',
+            'title' => 'duplicate',
+            'content' => '...',
+            'rendered_html' => '<p>...</p>',
+            'created_at' => now(),
+            'updated_at' => now(),
+        ]);
+    }
+
+    public function test_existing_documents_data_is_copied_to_translations(): void
+    {
+        // Roll the new migration back so the legacy columns exist again
+        \Illuminate\Support\Facades\Artisan::call('migrate:rollback', ['--step' => 1]);
+        $this->assertTrue(\Illuminate\Support\Facades\Schema::hasColumn('documents', 'title'));
+
+        // Seed a legacy document row directly
+        \Illuminate\Support\Facades\DB::table('documents')->insert([
+            'path' => 'Legacy.md',
+            'title' => 'Legacy Title',
+            'slug' => 'legacy-title',
+            'content' => '# Legacy body',
+            'rendered_html' => '<h1>Legacy body</h1>',
+            'file_size' => 0,
+            'file_hash' => str_repeat('0', 64),
+            'file_modified_at' => now(),
+            'created_at' => now(),
+            'updated_at' => now(),
+        ]);
+        $docId = \Illuminate\Support\Facades\DB::table('documents')->where('slug', 'legacy-title')->value('id');
+
+        // Re-run the migration
+        \Illuminate\Support\Facades\Artisan::call('migrate');
+
+        // Verify the data was copied to document_translations
+        $translation = \Illuminate\Support\Facades\DB::table('document_translations')
+            ->where('document_id', $docId)
+            ->first();
+
+        $this->assertNotNull($translation, 'Translation row should have been created from legacy data');
+        $this->assertSame('Legacy Title', $translation->title);
+        $this->assertSame('# Legacy body', $translation->content);
+        $this->assertSame('<h1>Legacy body</h1>', $translation->rendered_html);
+        $this->assertSame(config('app.locale', 'en'), $translation->locale);
+
+        // Verify documents.default_locale was set
+        $defaultLocale = \Illuminate\Support\Facades\DB::table('documents')->where('id', $docId)->value('default_locale');
+        $this->assertSame(config('app.locale', 'en'), $defaultLocale);
+    }
+}

src/tests/Feature/DocumentTranslationCrudTest.php

@@ -0,0 +1,94 @@
+<?php
+
+namespace Tests\Feature;
+
+use App\Models\Document;
+use App\Models\User;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+class DocumentTranslationCrudTest extends TestCase
+{
+    use RefreshDatabase;
+
+    public function test_owner_can_add_a_translation(): void
+    {
+        $owner = User::factory()->create();
+        $doc = Document::factory()->create(['default_locale' => 'en', 'created_by' => $owner->id]);
+
+        $response = $this->actingAs($owner)->post(
+            route('documents.translations.store', $doc),
+            ['locale' => 'ja', 'title' => 'こんにちは', 'content' => '本文']
+        );
+
+        $response->assertRedirect();
+        $this->assertNotNull($doc->fresh()->translationFor('ja', false));
+    }
+
+    public function test_non_owner_cannot_add_translation(): void
+    {
+        $owner = User::factory()->create();
+        $other = User::factory()->create();
+        $doc = Document::factory()->create(['default_locale' => 'en', 'created_by' => $owner->id]);
+
+        $response = $this->actingAs($other)->post(
+            route('documents.translations.store', $doc),
+            ['locale' => 'ja', 'title' => 'こんにちは', 'content' => '本文']
+        );
+
+        $response->assertForbidden();
+    }
+
+    public function test_invalid_locale_is_rejected(): void
+    {
+        $owner = User::factory()->create();
+        $doc = Document::factory()->create(['default_locale' => 'en', 'created_by' => $owner->id]);
+
+        $response = $this->actingAs($owner)->post(
+            route('documents.translations.store', $doc),
+            ['locale' => 'xx', 'title' => 'X', 'content' => 'Y']
+        );
+
+        $response->assertSessionHasErrors('locale');
+    }
+
+    public function test_duplicate_locale_returns_422(): void
+    {
+        $owner = User::factory()->create();
+        $doc = Document::factory()->create(['default_locale' => 'en', 'created_by' => $owner->id]);
+
+        $response = $this->actingAs($owner)->post(
+            route('documents.translations.store', $doc),
+            ['locale' => 'en', 'title' => 'X', 'content' => 'Y']
+        );
+
+        $response->assertStatus(422);
+    }
+
+    public function test_owner_can_delete_non_default_translation(): void
+    {
+        $owner = User::factory()->create();
+        $doc = Document::factory()->create(['default_locale' => 'en', 'created_by' => $owner->id]);
+        app(\App\Services\DocumentService::class)->addTranslation($doc, 'ja', 'JA', 'body', $owner->id);
+
+        $response = $this->actingAs($owner)->delete(
+            route('documents.translations.destroy', ['document' => $doc, 'locale' => 'ja'])
+        );
+
+        $response->assertRedirect();
+        $this->assertNull($doc->fresh()->translationFor('ja', false));
+    }
+
+    public function test_default_locale_translation_cannot_be_deleted(): void
+    {
+        $owner = User::factory()->create();
+        $doc = Document::factory()->create(['default_locale' => 'en', 'created_by' => $owner->id]);
+
+        $response = $this->actingAs($owner)->delete(
+            route('documents.translations.destroy', ['document' => $doc, 'locale' => 'en'])
+        );
+
+        $response->assertStatus(422);
+        $this->assertNotNull($doc->fresh()->translationFor('en', false));
+    }
+}

src/tests/Unit/Models/DocumentTest.php

@@ -0,0 +1,145 @@
+<?php
+
+namespace Tests\Unit\Models;
+
+use App\Models\Document;
+use App\Models\DocumentTranslation;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\App;
+use Tests\TestCase;
+
+class DocumentTest extends TestCase
+{
+    use RefreshDatabase;
+
+    public function test_title_accessor_returns_current_locale_translation(): void
+    {
+        $doc = Document::factory()->create(['default_locale' => 'en']);
+        $doc->translations()->where('locale', 'en')->update(['title' => 'Hello']);
+        DocumentTranslation::factory()->create([
+            'document_id' => $doc->id,
+            'locale' => 'ja',
+            'title' => 'こんにちは',
+        ]);
+
+        App::setLocale('ja');
+        $this->assertSame('こんにちは', $doc->fresh()->title);
+
+        App::setLocale('en');
+        $this->assertSame('Hello', $doc->fresh()->title);
+    }
+
+    public function test_title_accessor_falls_back_to_default_locale(): void
+    {
+        $doc = Document::factory()->create(['default_locale' => 'en']);
+        $doc->translations()->where('locale', 'en')->update(['title' => 'Hello']);
+
+        App::setLocale('ja');
+        $this->assertSame('Hello', $doc->fresh()->title);
+    }
+
+    public function test_content_and_rendered_html_accessors_fall_back(): void
+    {
+        $doc = Document::factory()->create(['default_locale' => 'en']);
+        $doc->translations()->where('locale', 'en')->update([
+            'content' => 'English body',
+            'rendered_html' => '<p>English body</p>',
+        ]);
+
+        App::setLocale('ja');
+        $fresh = $doc->fresh();
+        $this->assertSame('English body', $fresh->content);
+        $this->assertSame('<p>English body</p>', $fresh->rendered_html);
+    }
+
+    public function test_is_fallback_returns_true_when_locale_missing(): void
+    {
+        $doc = Document::factory()->create(['default_locale' => 'en']);
+        $this->assertTrue($doc->isFallback('ja'));
+        $this->assertFalse($doc->isFallback('en'));
+    }
+
+    public function test_translation_for_returns_null_when_fallback_disabled(): void
+    {
+        $doc = Document::factory()->create(['default_locale' => 'en']);
+        $this->assertNull($doc->translationFor('ja', fallback: false));
+        $this->assertNotNull($doc->translationFor('ja', fallback: true));
+    }
+
+    public function test_available_locales_lists_existing_translations(): void
+    {
+        $doc = Document::factory()->create(['default_locale' => 'en']);
+        DocumentTranslation::factory()->create(['document_id' => $doc->id, 'locale' => 'ja']);
+        DocumentTranslation::factory()->create(['document_id' => $doc->id, 'locale' => 'fr']);
+
+        $locales = $doc->fresh()->availableLocales();
+        sort($locales);
+        $this->assertSame(['en', 'fr', 'ja'], $locales);
+    }
+
+    public function test_sync_links_creates_outgoing_links_with_resolved_targets(): void
+    {
+        $target = Document::factory()->create(['default_locale' => 'en']);
+        $target->translations()->where('locale', 'en')->update(['title' => 'Target']);
+
+        $source = Document::factory()->create(['default_locale' => 'en']);
+        $source->translations()->where('locale', 'en')->update([
+            'content' => 'See [[Target]] for details.',
+        ]);
+
+        $source->fresh('translations')->syncLinks();
+
+        $links = $source->fresh()->outgoingLinks;
+        $this->assertCount(1, $links);
+        $this->assertSame($target->id, $links->first()->target_document_id);
+        $this->assertSame('Target', $links->first()->target_title);
+    }
+
+    public function test_sync_links_records_unresolved_links_with_null_target(): void
+    {
+        $source = Document::factory()->create();
+        $source->translations()->first()->update([
+            'content' => 'Goes to [[NoSuchPage]].',
+        ]);
+
+        $source->fresh('translations')->syncLinks();
+
+        $links = $source->fresh()->outgoingLinks;
+        $this->assertCount(1, $links);
+        $this->assertNull($links->first()->target_document_id);
+    }
+
+    public function test_process_links_replaces_wiki_link_with_anchor_keeping_label(): void
+    {
+        $target = Document::factory()->create(['default_locale' => 'en', 'slug' => 'target-doc']);
+        $target->translations()->where('locale', 'en')->update(['title' => 'Target']);
+        \Illuminate\Support\Facades\App::setLocale('ja');
+        \App\Models\DocumentTranslation::factory()->create([
+            'document_id' => $target->id,
+            'locale' => 'ja',
+            'title' => 'ターゲット',
+        ]);
+
+        $source = Document::factory()->create();
+        $source->translations()->first()->update([
+            'rendered_html' => '<p>See [[Target]].</p>',
+        ]);
+
+        $html = $source->fresh()->processLinks();
+
+        $this->assertStringContainsString('href="' . route('documents.show', 'target-doc') . '"', $html);
+        $this->assertStringContainsString('>Target<', $html); // label preserved
+        $this->assertStringContainsString('class="wiki-link"', $html);
+    }
+
+    public function test_process_links_marks_unresolved_links_as_new(): void
+    {
+        $source = Document::factory()->create();
+        $source->translations()->first()->update([
+            'rendered_html' => '<p>Click [[Ghost]].</p>',
+        ]);
+
+        $html = $source->fresh()->processLinks();
+        $this->assertStringContainsString('wiki-link-new', $html);
+    }
+}

src/tests/Unit/Models/DocumentTranslationTest.php

@@ -0,0 +1,55 @@
+<?php
+
+namespace Tests\Unit\Models;
+
+use App\Models\Document;
+use App\Models\DocumentTranslation;
+use Illuminate\Database\QueryException;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+class DocumentTranslationTest extends TestCase
+{
+    use RefreshDatabase;
+
+    public function test_belongs_to_a_document(): void
+    {
+        $doc = Document::factory()->create();
+        $translation = $doc->translations()->first();
+
+        $this->assertInstanceOf(Document::class, $translation->document);
+        $this->assertSame($doc->id, $translation->document->id);
+    }
+
+    public function test_unique_document_locale_constraint(): void
+    {
+        $doc = Document::factory()->create(['default_locale' => 'en']);
+
+        $this->expectException(QueryException::class);
+
+        DocumentTranslation::create([
+            'document_id' => $doc->id,
+            'locale' => 'en',
+            'title' => 'Duplicate',
+            'content' => 'x',
+            'rendered_html' => '<p>x</p>',
+        ]);
+    }
+
+    public function test_cascade_delete_when_document_deleted(): void
+    {
+        $doc = Document::factory()->create();
+        $translationId = $doc->translations()->first()->id;
+
+        $doc->forceDelete();
+
+        $this->assertNull(DocumentTranslation::find($translationId));
+    }
+
+    public function test_render_markdown_converts_basic_markdown(): void
+    {
+        $html = DocumentTranslation::renderMarkdown('# Hello');
+        $this->assertStringContainsString('<h1>', $html);
+        $this->assertStringContainsString('Hello', $html);
+    }
+}

src/tests/Unit/Services/DocumentServiceTest.php

@@ -0,0 +1,129 @@
+<?php
+
+namespace Tests\Unit\Services;
+
+use App\Models\Document;
+use App\Models\DocumentTranslation;
+use App\Models\User;
+use App\Services\DocumentService;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\App;
+use Tests\TestCase;
+
+class DocumentServiceTest extends TestCase
+{
+    use RefreshDatabase;
+
+    private DocumentService $service;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->service = new DocumentService();
+    }
+
+    public function test_create_document_creates_one_translation_in_given_locale(): void
+    {
+        App::setLocale('en'); // ensure deterministic
+        $user = User::factory()->create();
+
+        $doc = $this->service->createDocument('Hello', '# Hi', $user->id, 'en');
+
+        $this->assertSame('en', $doc->default_locale);
+        $this->assertSame('Hello.md', $doc->path);
+        $this->assertSame('hello', $doc->slug);
+        $this->assertCount(1, $doc->translations);
+        $this->assertSame('Hello', $doc->translations->first()->title);
+        $this->assertSame('# Hi', $doc->translations->first()->content);
+        $this->assertStringContainsString('<h1>', $doc->translations->first()->rendered_html);
+    }
+
+    public function test_update_document_in_default_locale_regenerates_path_and_slug(): void
+    {
+        $doc = $this->service->createDocument('Old', 'body', null, 'en');
+
+        $updated = $this->service->updateDocument($doc, 'New Title', 'body2', null, 'en');
+
+        $this->assertSame('New Title.md', $updated->path);
+        $this->assertSame('new-title', $updated->slug);
+    }
+
+    public function test_update_document_in_non_default_locale_does_not_change_path(): void
+    {
+        $doc = $this->service->createDocument('English', 'body', null, 'en');
+        $originalPath = $doc->path;
+        $originalSlug = $doc->slug;
+
+        $updated = $this->service->updateDocument($doc, '日本語タイトル', '本文', null, 'ja');
+
+        $this->assertSame($originalPath, $updated->path);
+        $this->assertSame($originalSlug, $updated->slug);
+        $this->assertSame('日本語タイトル', $updated->translationFor('ja', false)->title);
+    }
+
+    public function test_add_translation_creates_new_locale_row(): void
+    {
+        $doc = $this->service->createDocument('Hello', 'body', null, 'en');
+
+        $this->service->addTranslation($doc, 'ja', 'こんにちは', 'やあ', null);
+
+        $this->assertCount(2, $doc->fresh()->translations);
+        $this->assertSame('こんにちは', $doc->fresh()->translationFor('ja', false)->title);
+    }
+
+    public function test_add_translation_throws_on_duplicate_locale(): void
+    {
+        $doc = $this->service->createDocument('Hello', 'body', null, 'en');
+
+        $this->expectException(\InvalidArgumentException::class);
+        $this->service->addTranslation($doc, 'en', 'X', 'Y', null);
+    }
+
+    public function test_delete_translation_removes_non_default(): void
+    {
+        $doc = $this->service->createDocument('Hello', 'body', null, 'en');
+        $this->service->addTranslation($doc, 'ja', 'こんにちは', 'やあ', null);
+
+        $this->service->deleteTranslation($doc, 'ja');
+
+        $this->assertNull($doc->fresh()->translationFor('ja', false));
+    }
+
+    public function test_delete_translation_refuses_default_locale(): void
+    {
+        $doc = $this->service->createDocument('Hello', 'body', null, 'en');
+
+        $this->expectException(\InvalidArgumentException::class);
+        $this->service->deleteTranslation($doc, 'en');
+    }
+
+    public function test_set_default_locale_requires_existing_translation(): void
+    {
+        $doc = $this->service->createDocument('Hello', 'body', null, 'en');
+
+        $this->expectException(\InvalidArgumentException::class);
+        $this->service->setDefaultLocale($doc, 'ja');
+    }
+
+    public function test_set_default_locale_regenerates_path_from_new_locale_title(): void
+    {
+        $doc = $this->service->createDocument('Hello', 'body', null, 'en');
+        $this->service->addTranslation($doc, 'ja', 'こんにちは', 'やあ', null);
+
+        $updated = $this->service->setDefaultLocale($doc, 'ja');
+
+        $this->assertSame('ja', $updated->default_locale);
+        $this->assertSame('こんにちは.md', $updated->path);
+    }
+
+    public function test_search_returns_distinct_documents_across_locales(): void
+    {
+        $doc = $this->service->createDocument('Searchword', 'body', null, 'en');
+        $this->service->addTranslation($doc, 'ja', 'Searchword JA', 'Searchword body', null);
+
+        $results = $this->service->search('Searchword');
+
+        $this->assertCount(1, $results); // distinct, even though 2 translations match
+        $this->assertSame($doc->id, $results->first()->id);
+    }
+}

src/tests/Unit/Services/WikiLinkResolverTest.php

@@ -0,0 +1,88 @@
+<?php
+
+namespace Tests\Unit\Services;
+
+use App\Models\Document;
+use App\Models\DocumentTranslation;
+use App\Services\WikiLinkResolver;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+class WikiLinkResolverTest extends TestCase
+{
+    use RefreshDatabase;
+
+    private WikiLinkResolver $resolver;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->resolver = new WikiLinkResolver();
+    }
+
+    public function test_resolves_via_current_locale_title(): void
+    {
+        $doc = Document::factory()->create(['default_locale' => 'en', 'slug' => 'getting-started']);
+        $doc->translations()->where('locale', 'en')->update(['title' => 'Getting Started']);
+        DocumentTranslation::factory()->create([
+            'document_id' => $doc->id,
+            'locale' => 'ja',
+            'title' => 'はじめに',
+        ]);
+
+        $resolved = $this->resolver->resolve('はじめに', 'ja');
+        $this->assertSame($doc->id, $resolved->id);
+    }
+
+    public function test_resolves_via_default_locale_when_current_locale_missing(): void
+    {
+        $doc = Document::factory()->create(['default_locale' => 'en']);
+        $doc->translations()->where('locale', 'en')->update(['title' => 'Getting Started']);
+
+        $resolved = $this->resolver->resolve('Getting Started', 'ja');
+        $this->assertSame($doc->id, $resolved->id);
+    }
+
+    public function test_resolves_via_any_locale_deterministically(): void
+    {
+        // Two documents both have a 'fr' translation titled "Bonjour", neither is current/default
+        $docA = Document::factory()->create(['default_locale' => 'en']);
+        DocumentTranslation::factory()->create(['document_id' => $docA->id, 'locale' => 'fr', 'title' => 'Bonjour']);
+
+        $docB = Document::factory()->create(['default_locale' => 'en']);
+        DocumentTranslation::factory()->create(['document_id' => $docB->id, 'locale' => 'fr', 'title' => 'Bonjour']);
+
+        $resolved = $this->resolver->resolve('Bonjour', 'ja');
+        // Lower id wins (deterministic)
+        $this->assertSame($docA->id, $resolved->id);
+    }
+
+    public function test_resolves_via_slug_when_no_title_match(): void
+    {
+        $doc = Document::factory()->create(['slug' => 'unique-slug', 'default_locale' => 'en']);
+        $doc->translations()->where('locale', 'en')->update(['title' => 'Whatever']);
+
+        $resolved = $this->resolver->resolve('unique-slug', 'ja');
+        $this->assertSame($doc->id, $resolved->id);
+    }
+
+    public function test_returns_null_when_nothing_matches(): void
+    {
+        $this->assertNull($this->resolver->resolve('Nonexistent', 'en'));
+    }
+
+    public function test_current_locale_wins_over_default(): void
+    {
+        // Doc A has en title "Setup"; Doc B has ja title "Setup"
+        $docA = Document::factory()->create(['default_locale' => 'en']);
+        $docA->translations()->where('locale', 'en')->update(['title' => 'Setup']);
+
+        $docB = Document::factory()->create(['default_locale' => 'en']);
+        $docB->translations()->where('locale', 'en')->update(['title' => 'Different']);
+        DocumentTranslation::factory()->create(['document_id' => $docB->id, 'locale' => 'ja', 'title' => 'Setup']);
+
+        // Browsing in ja: ja-locale match (Doc B) should win over default-locale match (Doc A)
+        $resolved = $this->resolver->resolve('Setup', 'ja');
+        $this->assertSame($docB->id, $resolved->id);
+    }
+}