Localization L10n

This walks Claude through proper localization implementation, covering everything from i18next and react-i18next setup to RTL support and regional formatting. You get concrete patterns for organizing translation files by namespace and locale, handling regional variants with fallback chains (like es-MX to es to en), and using Intl APIs for dates, numbers, and currency. It covers the cultural adaptation stuff too, like text expansion planning (30-50% from English), address format variations, and pseudolocalization for testing. Honestly most useful when you're past the basic i18n setup and need to handle real-world complexity like supporting both en-US and en-GB with proper fallbacks, or making sure your layouts don't break when German translations blow up your button text.