- Create useLanguage() hook following useCurrency/useWeightUnit pattern
- Update formatPrice() to use Intl.NumberFormat for locale-aware currency display
- Update formatWeight() to use Intl.NumberFormat for locale-aware number formatting
- Update formatDualPrice() to pass locale through
- Update useFormatters() to pass locale to all formatters
- Add formatter tests for en/de locales (15 tests passing)
Phase 34, Plan 03
