Add documents.delete_translation lang key for editor button

The editor's delete-translation button used `__('messages.documents.delete_translation') ?? __('messages.documents.delete')`, but `__()` returns the key string (not null) on miss so the `??` fallback never fires — the button rendered the literal key. Adds the missing key to all 16 locales (en+ja human-translated, others mirror en) and simplifies the blade to a single `__()` call.

Plan doc also reflects the SQLite dropIndex requirement found during Task 2.

docs/superpowers/plans/2026-05-10-article-i18n.md

@@ -369,8 +369,10 @@ return new class extends Migration
             DB::statement('ALTER TABLE documents DROP INDEX documents_search_index');
         }
 
-        // 5. Drop translatable columns from documents
+        // 5. Drop translatable columns from documents.
+        //    SQLite requires explicit dropIndex on the title index before dropColumn.
         Schema::table('documents', function (Blueprint $table) {
+            $table->dropIndex(['title']);
             $table->dropColumn(['title', 'content', 'rendered_html']);
         });
     }

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

@@ -3,65 +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 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 $fillable = [
         'path',
-        'title',
         'slug',
-        'content',
-        'rendered_html',
+        'default_locale',
         'frontmatter',
         'file_size',
         'file_hash',
@@ -70,11 +30,6 @@ public function resolveRouteBinding($value, $field = null)
         'updated_by',
     ];
 
-    /**
-     * Get the attributes that should be cast.
-     *
-     * @return array<string, string>
-     */
     protected function casts(): array
     {
         return [
@@ -83,192 +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(
@@ -281,57 +108,142 @@ public function recentByUsers(): HasManyThrough
         );
     }
 
-    /**
-     * Translations of this document, one per locale.
-     * (Other relation/accessor refactor lands in Task 4.)
-     */
-    public function translations(): \Illuminate\Database\Eloquent\Relations\HasMany
+    // ----- Translation helpers -----
+
+    public function translationFor(string $locale, bool $fallback = true): ?DocumentTranslation
     {
-        return $this->hasMany(DocumentTranslation::class);
+        $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/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/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' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        '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' => 'Zurück zur Startseite',
     ],
 
+    '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' => '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' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        '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' => 'Volver al inicio',
     ],
 
+    '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' => 'Perfil',

src/lang/fr/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Contenu',
         'content_placeholder' => 'Écrivez votre markdown ici...',
         'saving' => 'Enregistrement...',
+        'fallback_notice' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        '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' => 'Retour à l\'accueil',
     ],
 
+    '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' => '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' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        '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
@@ -124,6 +132,25 @@
         'back_to_home' => 'होम पर वापस जाएं',
     ],
 
+    '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' => 'प्रोफ़ाइल',

src/lang/it/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Contenuto',
         'content_placeholder' => 'Scrivi il tuo markdown qui...',
         'saving' => 'Salvataggio...',
+        'fallback_notice' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        '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
@@ -124,6 +132,25 @@
         'back_to_home' => 'Torna alla 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' => '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' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        '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' => '홈으로 돌아가기',
     ],
 
+    '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' => '프로필',

src/lang/pl/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Treść',
         'content_placeholder' => 'Napisz swój markdown tutaj...',
         'saving' => 'Zapisywanie...',
+        'fallback_notice' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        '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
@@ -124,6 +132,25 @@
         'back_to_home' => 'Wróć do strony głównej',
     ],
 
+    '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' => 'Profil',

src/lang/pt-BR/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Conteúdo',
         'content_placeholder' => 'Escreva seu markdown aqui...',
         'saving' => 'Salvando...',
+        'fallback_notice' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        '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
@@ -124,6 +132,25 @@
         'back_to_home' => 'Voltar para Início',
     ],
 
+    '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' => 'Perfil',

src/lang/ru/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Содержимое',
         'content_placeholder' => 'Напишите здесь ваш markdown...',
         'saving' => 'Сохранение...',
+        'fallback_notice' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        '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
@@ -124,6 +132,25 @@
         'back_to_home' => 'Вернуться на главную',
     ],
 
+    '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' => 'Профиль',

src/lang/tr/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'İçerik',
         'content_placeholder' => 'Markdown\'ınızı buraya yazın...',
         'saving' => 'Kaydediliyor...',
+        'fallback_notice' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        '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
@@ -124,6 +132,25 @@
         'back_to_home' => 'Ana Sayfaya Dön',
     ],
 
+    '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' => 'Profil',

src/lang/uk/messages.php

@@ -39,6 +39,14 @@
         'content_label' => 'Вміст',
         'content_placeholder' => 'Напишіть тут ваш markdown...',
         'saving' => 'Збереження...',
+        'fallback_notice' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        '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
@@ -124,6 +132,25 @@
         'back_to_home' => 'Повернутися на головну',
     ],
 
+    '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' => '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' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        '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
@@ -124,6 +132,25 @@
         'back_to_home' => 'Quay lại trang chủ',
     ],
 
+    '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' => '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' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        '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' => '返回首页',
     ],
 
+    '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' => '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' => 'A translation in your selected language is not available. Showing the :locale version.',
+        'add_translation' => 'Add translation',
+        'translation_added' => 'Translation added.',
+        'translation_deleted' => 'Translation deleted.',
+        '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' => '返回首頁',
     ],
 
+    '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' => '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.' . $loc, [], 'en') }}
+                        @if($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, [], 'en') }}
+                        <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/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/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);
+    }
+}