feat: Add multilingual README support

PULL_REQUEST.md

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+# Add Multilingual README Support
+
+## Summary
+
+This PR adds support for multilingual README files in HACS. Users will automatically see content in their Home Assistant language setting if available, with fallback to default English content.
+
+## Changes
+
+1. **Multilingual README Support**
+   - Added `async_get_info_file_contents_with_language()` method
+   - Supports `README.{language_code}.md` files (e.g., `README.de.md`, `README.fr.md`)
+   - Automatic language detection with fallback to `README.md`
+
+2. **Manifest Updates**
+   - Renamed `supported_languages` to `content_languages` in `hacs.json` manifest
+   - Updated validator to use `content_languages` key
+   - Validates language codes and checks for corresponding README files
+
+3. **WebSocket Handler Updates**
+   - Extended `hacs/repository/info` to use language parameter for README content
+
+## Related PRs
+
+- **Frontend PR:** https://github.com/hacs/frontend/pull/XXX
+- **Documentation PR:** https://github.com/hacs/documentation/pull/660
+
+## Checklist
+
+- [x] Code follows project style guidelines
+- [x] Changes are backward compatible
+- [x] Code tested locally
+- [x] Validators updated
+- [x] WebSocket handlers updated
+
+## Notes
+
+- Repository maintainers can provide multilingual README files using `README.{language_code}.md` (e.g., `README.de.md`, `README.fr.md`)
+- Language codes must be 2-letter ISO 639-1 codes (e.g., `de`, `fr`, `es`)
+- The `content_languages` key in `hacs.json` can optionally declare supported languages for validation
+