# 12 — Internationalization (i18n)

## Overview
- **Default Locale**: `de` (Deutsch), fallback `en` (English).
- **Supported Locales**: MVP focuses on `de` and `en`; expandable via config/app.php locales array.
- **Strategy**: Hybrid approach – Laravel PHP for backend/Blade views, react-i18next for React/Vite PWAs (Marketing, Tenant Admin, Guest).
- **Translatable Fields**: JSON columns in DB for dynamic content (e.g., `name`, `description`, `title`, `body_markdown` in models like Package, EventType, LegalPage).
- **Namespaces**: Organized by feature (e.g., `marketing`, `auth`, `guest`, `admin`) to avoid key collisions; glossary terms centralized in a shared namespace if needed.
- **Date/Number Formatting**: Locale-aware via Laravel's Carbon/Intl; PWAs use Intl API or date-fns with locale bundles.
- **RTL Support**: Not in MVP; future via CSS classes and i18next RTL plugin.
- **SEO**: Multilingual URLs with prefixes (/de/, /en/), hreflang tags, canonical links, translated meta (title, description, og:).

## Backend (Laravel/PHP)
- **Config**: `config/app.php` – `locale => 'de'`, `fallback_locale => 'en'`, `available_locales => ['de', 'en']`.
- **Translation Files**:
  - PHP arrays: `resources/lang/{locale}/{group}.php` (e.g., `marketing.php`, `auth.php`, `legal.php`) for Blade and API responses.
  - JSON for PWAs: `public/lang/{locale}/{namespace}.json` (e.g., `public/lang/de/marketing.json`) – migrated from PHP where possible; loaded via dedicated route.
- **Routing**:
  - Prefixed groups: `Route::prefix('{locale?}')->where(['locale' => 'de|en'])->middleware('SetLocale')` in `routes/web.php`.
  - Fallbacks: Non-prefixed routes redirect to `/de/{path}` (e.g., `/login` → `/de/login`).
  - Auth routes (login, register, logout): Prefixed and named (e.g., `Route::get('/login', ...)->name('login')`).
  - API routes: Locale from header/session; no URL prefix for `/api/v1`.
- **Middleware**: `SetLocale` – Extracts locale from URL segment(1), sets `App::setLocale()`, stores in session; defaults to 'de'.
- **JSON Loader Route**: `Route::get('/lang/{locale}/{namespace}.json', ...)` – Serves from `public_path('lang/{locale}/{namespace}.json')`; Vite proxy forwards requests.
- **DB Translations**: Use JSON fields with spatie/laravel-translatable or native casts; admin UI (Filament) for editing per locale.
- **Legal Pages**: Dynamic via LegalPage model; rendered with `__($key)` or JSON for PWAs.

## Frontend (React/Vite PWAs)
- **Library**: react-i18next with i18next-http-backend for async JSON loads.
- **Setup** (`resources/js/i18n.js`):
  - Init: `i18n.use(Backend).use(LanguageDetector).init({ lng: 'de', fallbackLng: 'en', ns: ['marketing', 'auth'], backend: { loadPath: '/lang/{{lng}}/{{ns}}.json' } })`.
  - Detection: Path-based (`order: ['path']`, `lookupFromPathIndex: 0`) for prefixed URLs; cookie/session fallback.
  - Provider: Wrap `<App>` in `<I18nextProvider i18n={i18n}>` in `app.tsx`.
- **Usage**:
  - Hook: `const { t } = useTranslation('namespace');` in components (e.g., `t('marketing.home.title')`).
  - Interpolation: Placeholders `{count}`; pluralization via i18next rules.
  - Dynamic Keys: Avoid; use namespaces for organization.
- **Inertia Integration**:
  - Page Resolver: `resolvePageComponent(`./Pages/${name}.tsx`, import.meta.glob('./Pages/**/*.tsx'))` – Matches capital 'Pages' directory.
  - Props: Pass `locale` from middleware to pages.
  - Links: `<Link href={`/${locale}/path`}>` for prefixed navigation (e.g., Header.tsx).
- **Marketing Frontend**:
  - Namespaces: `marketing` (Home, Packages, Blog, Features), `auth` (Login, Register).
  - Components: All hard-coded strings replaced (e.g., Home.tsx: `t('marketing.hero.title')`); SEO meta via `Head` with `t()`.
  - Header: Locale selector; dynamic links (e.g., `/${locale}/login` with `t('auth.header.login')`).
- **Guest/Tenant PWAs**:
  - Similar setup; load JSON on app init.
  - Guest: Anonymous, locale from URL or default 'de'; strings for UI (e.g., gallery, upload).
  - Tenant Admin: User-preferred locale from profile; sync with backend.
- **Automation**:
  - Extraction: i18next-scanner (npm script: `i18next-scanner --config i18next-scanner.config.js`) to scan TSX for `t('key')` and update JSON.
  - Validation: Missing keys log warnings; dev mode strict.

## SEO & Accessibility
- **Multilingual URLs**: `/de/home`, `/en/home`; 301 redirects for non-prefixed.
- **Hreflang**: `<link rel="alternate" hreflang="de" href="/de/home">` in `<Head>`.
- **Canonical**: `<link rel="canonical" href={currentUrl}>` based on detected locale.
- **Meta**: Translated via `t('seo.title')`; og:locale='de_DE'.
- **Sitemap**: Generate with `de/` and `en/` variants; update `public/sitemap.xml`.
- **Robots.txt**: Allow both locales; noindex for dev.
- **Accessibility**: ARIA labels with `t()`; screen reader support for language switches.

## Migration from PHP to JSON
- Extract keys from `resources/lang/{locale}/marketing.php` to `public/lang/{locale}/marketing.json`.
- Consolidate: Remove duplicates; use nested objects (e.g., `{ "header": { "login": "Anmelden" } }`).
- Fallback: PHP arrays remain for backend; JSON for PWAs.

## Testing & Maintenance
- **Tests**: PHPUnit for backend (`__('key')`); Vitest/Jest for frontend (`t('key')` renders correctly).
- **Linting**: ESLint rule for missing translations; i18next-scanner in pre-commit.
- **Deployment**: JSON files in public; cache-bust via Vite hashes.
- **Expansion**: Add locales via config; migrate more namespaces (e.g., `guest`, `admin`).

## Decisions & Trade-offs
- Path-based detection over query params for SEO/clean URLs.
- JSON over PHP for PWAs: Faster async loads, no server roundtrips.
- No auto-redirect on locale mismatch in MVP; user chooses via selector.
- ADR: Use react-i18next over next-intl (Inertia compatibility).
