feat(i18n): add French language support and enhance localization

- Introduced French as a supported language across the application, updating locale files and adding translations for various components.
- Enhanced language handling logic to accommodate French, ensuring proper detection and fallback mechanisms.
- Updated UI elements to include French language options, improving accessibility for French-speaking users.
- Refactored SEO handling to include French in hreflang links, enhancing search engine indexing for multilingual content.
- Added new scripts for managing French translations and ensuring consistency across language files.

.gitignore

@@ -17,6 +17,8 @@ frontend/node_modules
 frontend/node_modules/*
 frontend/dist
 frontend/dist/*
+frontend/scripts/.i18n-de-fr-cache.json
+frontend/scripts/.falukant-fr-smooth-cache.json
 frontedtree.txt
 backend/dist/
 backend/data/model-cache