Show fallback banner when current-locale translation is missing

DocumentViewer computes viewLocale and isFallback at mount; banner
links authenticated owners to the editor for the current UI locale.
Adds documents.fallback_notice + locale_names to all 16 lang files
(en+ja human-translated, others mirror en for now).

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/lang/de/messages.php

@@ -39,6 +39,13 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -123,6 +130,25 @@
         '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

@@ -41,6 +41,11 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -125,6 +130,25 @@
         '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 +39,13 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -123,6 +130,25 @@
         '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 +39,13 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -123,6 +130,25 @@
         '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 +39,13 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -124,6 +131,25 @@
         '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 +39,13 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -124,6 +131,25 @@
         '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

@@ -41,6 +41,11 @@
         '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_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
@@ -125,6 +130,14 @@
         '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 +39,13 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -123,6 +130,25 @@
         '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 +39,13 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -124,6 +131,25 @@
         '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 +39,13 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -124,6 +131,25 @@
         '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 +39,13 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -124,6 +131,25 @@
         '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 +39,13 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -124,6 +131,25 @@
         '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 +39,13 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -124,6 +131,25 @@
         '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 +39,13 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -124,6 +131,25 @@
         '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 +39,13 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -123,6 +130,25 @@
         '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 +39,13 @@
         '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_blocked' => 'The default-language translation cannot be deleted.',
+        'translation_tabs_label' => 'Languages',
     ],
 
     // Quick Switcher
@@ -123,6 +130,25 @@
         '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-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/tests/Feature/DocumentI18nTest.php

@@ -0,0 +1,68 @@
+<?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'));
+    }
+}