RustyCMS: File-based headless CMS with REST API, admin UI, multilingual support

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/multilingual.md

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+# Multilingual (i18n)
+
+## Recommended approach: Locale as folder (implemented)
+
+Content per language in separate folders:
+
+```
+content/
+  de/
+    page/
+      home.json5
+      about.json5
+    post/
+      example-post.json5
+  en/
+    page/
+      home.json5
+      about.json5
+    post/
+      example-post.json5
+```
+
+- **Same slug per language** (e.g. `home` in DE and EN).
+- **API:** `?_locale=de` or `?_locale=en`. If parameter is missing, default locale is used.
+- **Configuration:** `RUSTYCMS_LOCALES=de,en` enables the mode; **first locale = default** (e.g. `de`).
+- **Without `RUSTYCMS_LOCALES`:** Previous behavior (single language). Content remains under `content/{collection}/` (no locale folder).
+
+## Activation
+
+```bash
+# .env or export
+RUSTYCMS_LOCALES=de,en
+```
+
+On startup you'll see e.g.: `Multilingual: locales ["de", "en"] (default: de)`.
+
+## API usage
+
+```bash
+# Default locale (first in RUSTYCMS_LOCALES, e.g. de)
+GET /api/content/page/home
+
+# Explicit locale
+GET /api/content/page/home?_locale=en
+GET /api/content/page?_page=1&_per_page=50&_locale=en
+```
+
+Response still has the same structure; only the content is locale-dependent. For POST/PUT/DELETE, `_locale` can be passed as a query parameter so the entry is created/updated/deleted in the correct locale.
+
+## Optional extensions
+
+- **page_config per locale:** e.g. `content/de/page_config/default.json5` and `content/en/page_config/default.json5` for locale-specific SEO, footer text, etc.
+- **Available locales in API:** e.g. `GET /api/locales` → `["de","en"]` (from config).
+- **hreflang / languageAlternates:** derive in frontend from page config or known locales (e.g. already considered in `@types/SeoProps.ts`).
+
+## Alternatives (not implemented)
+
+- **Locale as field in entry:** Entry with `locale: "de"`, slug unique per language (e.g. `home-de`, `home-en`). Works without store changes, but same logical content has different slugs.
+- **Translations in one entry:** File with `translations: { de: {...}, en: {...} }`. No extra folders, but schema and API (filter, resolve) become more complex.