core: implement multi-language support (i18n)

[EmeditWeb]

Problem

StepFi targets learners in emerging markets across
Africa. The app is English-only.

What To Build

1. Install i18next and react-i18next
2. French and Portuguese translations
3. Language detection (default to device)
4. RTL groundwork for future Arabic
5. Locale-aware formatting

Files To Touch

• src/locales/ (new)
• hooks/useTranslation.ts (new)
• All screen files
• app/(tabs)/settings.tsx

Acceptance Criteria

• All UI text translatable
• French translation complete
• Portuguese translation complete
• Language persists on app restart
• npx expo export --platform web passes

Mandatory Checks Before PR

• npx expo export --platform web passes
• No hardcoded user-facing strings
• PR references this issue

[BigElv]

I would love to work on this

[OG-wura]

hello mainainer. i would love to work on this

[grantfox-oss]

🦊 GrantFox — @OG-wura has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #19)
2. Your PR will be reviewed by the StepFi-app maintainers

Good luck! Track your progress on GrantFox.