chore: upgrade i18n-js from 3.x to 4.x

[hb2708]

Summary

Upgrade i18n-js from 3.5.1 to 4.x. Version 4 is a complete rewrite with a new class-based API that affects all translation calls across the app.

Current → Target

Package	Current	Latest
i18n-js	3.5.1	4.5.2
@types/i18n-js	3.0.2	4.0.1

Why Upgrade

• v3 is no longer maintained
• v4 has improved TypeScript support, better pluralization, and a cleaner API
• Fixes known issues with locale fallback behavior

Migration Steps

1. Install new version:

   yarn add i18n-js@latest
   yarn add --dev @types/i18n-js@latest

2. Update initialization — v4 uses a class-based API:

   // Before (v3)
   import I18n from 'i18n-js';
   I18n.translations = { en: { ... }, fr: { ... } };
   I18n.locale = 'en';
   
   // After (v4)
   import { I18n } from 'i18n-js';
   const i18n = new I18n({ en: { ... }, fr: { ... } });
   i18n.locale = 'en';

3. Update all t() calls — ensure they use the new instance:

   // Before: I18n.t('key')
   // After:  i18n.t('key')

4. Review pluralization — v4 has a different pluralization system
5. Search codebase for all imports: grep -r "i18n-js" app/
6. Run yarn ci to verify

Files Likely Affected

• Translation initialization file (locale setup)
• Every component/screen that calls I18n.t() or imports from i18n-js
• Any custom locale/fallback configuration

References

• i18n-js v4 Migration Guide
• Changelog