feat: add multi-language (i18n) support for vendor dashboard and storefront

- Add database fields for language preferences:
  - Vendor: dashboard_language, storefront_language, storefront_languages
  - User: preferred_language
  - Customer: preferred_language

- Add language middleware for request-level language detection:
  - Cookie-based persistence
  - Browser Accept-Language fallback
  - Vendor storefront language constraints

- Add language API endpoints (/api/v1/language/*):
  - POST /set - Set language preference
  - GET /current - Get current language info
  - GET /list - List available languages
  - DELETE /clear - Clear preference

- Add i18n utilities (app/utils/i18n.py):
  - JSON-based translation loading
  - Jinja2 template integration
  - Language resolution helpers

- Add reusable language selector macros for templates
- Add languageSelector() Alpine.js component
- Add translation files (en, fr, de, lb) in static/locales/
- Add architecture rules documentation for language implementation
- Update marketplace-product-detail.js to use native language names

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

static/vendor/js/init-alpine.js

@@ -118,4 +118,50 @@ function data() {
             }
         }
     };
-}
+}
+
+/**
+ * Language Selector Component
+ * Alpine.js component for language switching in vendor dashboard
+ */
+function languageSelector(currentLang, enabledLanguages) {
+    return {
+        isLangOpen: false,
+        currentLang: currentLang || 'fr',
+        languages: enabledLanguages || ['en', 'fr', 'de', 'lb'],
+        languageNames: {
+            'en': 'English',
+            'fr': 'Français',
+            'de': 'Deutsch',
+            'lb': 'Lëtzebuergesch'
+        },
+        languageFlags: {
+            'en': 'gb',
+            'fr': 'fr',
+            'de': 'de',
+            'lb': 'lu'
+        },
+        async setLanguage(lang) {
+            if (lang === this.currentLang) {
+                this.isLangOpen = false;
+                return;
+            }
+            try {
+                const response = await fetch('/api/v1/language/set', {
+                    method: 'POST',
+                    headers: { 'Content-Type': 'application/json' },
+                    body: JSON.stringify({ language: lang })
+                });
+                if (response.ok) {
+                    this.currentLang = lang;
+                    window.location.reload();
+                }
+            } catch (error) {
+                console.error('Failed to set language:', error);
+            }
+            this.isLangOpen = false;
+        }
+    };
+}
+
+window.languageSelector = languageSelector;

static/vendor/js/letzshop.js

@@ -73,6 +73,11 @@ function vendorLetzshop() {
             tracking_carrier: ''
         },
 
+        // Export
+        exportLanguage: 'fr',
+        exportIncludeInactive: false,
+        exporting: false,
+
         async init() {
             // Guard against multiple initialization
             if (window._vendorLetzshopInitialized) {
@@ -410,6 +415,68 @@ function vendorLetzshop() {
             if (!dateStr) return 'N/A';
             const date = new Date(dateStr);
             return date.toLocaleDateString() + ' ' + date.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' });
+        },
+
+        /**
+         * Download product export CSV
+         */
+        async downloadExport() {
+            this.exporting = true;
+            this.error = '';
+
+            try {
+                const params = new URLSearchParams({
+                    language: this.exportLanguage,
+                    include_inactive: this.exportIncludeInactive.toString()
+                });
+
+                // Get the token for authentication
+                const token = localStorage.getItem('wizamart_token');
+                if (!token) {
+                    throw new Error('Not authenticated');
+                }
+
+                const response = await fetch(`/api/v1/vendor/letzshop/export?${params}`, {
+                    method: 'GET',
+                    headers: {
+                        'Authorization': `Bearer ${token}`
+                    }
+                });
+
+                if (!response.ok) {
+                    const errorData = await response.json().catch(() => ({}));
+                    throw new Error(errorData.detail || 'Export failed');
+                }
+
+                // Get filename from Content-Disposition header
+                const contentDisposition = response.headers.get('Content-Disposition');
+                let filename = `letzshop_export_${this.exportLanguage}.csv`;
+                if (contentDisposition) {
+                    const match = contentDisposition.match(/filename="(.+)"/);
+                    if (match) {
+                        filename = match[1];
+                    }
+                }
+
+                // Download the file
+                const blob = await response.blob();
+                const url = window.URL.createObjectURL(blob);
+                const link = document.createElement('a');
+                link.href = url;
+                link.download = filename;
+                document.body.appendChild(link);
+                link.click();
+                document.body.removeChild(link);
+                window.URL.revokeObjectURL(url);
+
+                this.successMessage = `Export downloaded: ${filename}`;
+            } catch (error) {
+                console.error('[VENDOR LETZSHOP] Export failed:', error);
+                this.error = error.message || 'Failed to export products';
+            } finally {
+                this.exporting = false;
+                setTimeout(() => this.successMessage = '', 5000);
+            }
         }
     };
 }