🌍 fix: Enhance i18n Support & Optimize Category Handling

[rubentalstra]

Summary

This PR improves internationalization (i18n) support by adding new translations and refining category management with localization-friendly keys.

Closes: #5846
Closes: #5858
Closes: #5865

Docs: LibreChat-AI/librechat.ai#235

🔍 Changes

• 🌎 i18n Enhancements

  • Added Estonian (et-EE) language support across multiple files.
  • Standardized Chinese variants:
    • zh-Hans (Simplified)
    • zh-Hant (Traditional)
  • Improved fallback logic in i18n.ts for better language detection.
  • Updated UI category labels to use translation keys instead of hardcoded values.

• 🏷️ Category Management

  • Refactored category values (Categories.js) to use com_ui_ prefixed keys.
  • Updated useCategories.tsx to use type-safe localization keys (TranslationKeys).

• 🛠️ Refactoring & Optimization

  • 📌 Improved detection of unused translation keys in .github/workflows/i18n-unused-keys.yml, now scanning the api/ directory.
  • 🧹 Removed redundant memoizedLocalize function in useLocalize.ts for better maintainability.

• 📦 Dependency Update

  • Added i18next-browser-languagedetector to package.json.

✅ Status

• Ready for review 🚀

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Change Type

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• This change requires a documentation update

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Testing

Test Configuration:

• Ensured i18n translations load correctly with new keys and fallback logic.
• Verified unused key detection includes api/ directory in GitHub workflow.
• Tested category labels reflect correct translations across the UI.

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Checklist

• My code adheres to this project's style guidelines.
• I have performed a self-review of my own code.
• I have commented in any complex areas of my code.
• I have made pertinent documentation changes.
• My changes do not introduce new warnings.
• Local unit tests pass with my changes.
• Any changes dependent on mine have been merged and published in downstream modules.
• A pull request for updating the documentation has been submitted.