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.

frontend/src/i18n/locales/fr/message.json

@@ -0,0 +1,8 @@
+{
+    "message": {
+        "title": "avis",
+        "close": "Fermer",
+        "test": "Travaux d'essai",
+        "success": "L'action a été couronnée de succès."
+    }
+}