Implement internationalization (i18n) and localization including message extraction, translation catalogs, pluralization rules, date/time/number formatting, RTL language support, and i18n libraries like i18next and gettext. Use for multi-language, translation, or localization needs.

Internationalization (i18n) & Localization Table of Contents [Overview]( overview) [When to Use]( when to use) [Quick Start]( quick start) [Reference Guides]( reference guides) [Best Practices]( best practices) Overview Comprehensive guide to implementing internationalization and localization in applications. Covers message translation, pluralization, date/time/number formatting, RTL languages, and integration with popular i18n libraries. When to Use Building multi language applications Supporting international users Implementing language switching Formatting dates, times, and numbers for different locales Supporting RTL (right to left) languages Extracting and managing translation strings Implementing pluralization rules Setting up translation workflows Quick Start Minimal working example: Reference Guides Detailed implementations in the references/ directory: Guide Contents [i18next (JavaScript/TypeScript)](references/i18next javascripttypescript.md) i18next (JavaScript/TypeScript) [React Intl (Format.js)](references/react intl formatjs.md) React Intl (Format.js) [Python i18n (gettext)](references/python i18n gettext.md) Python i18n (gettext) [Date and Time Formatting](references/date and time formatting.md) Date and Time Formatting [Number and Currency Formatting](references/number and currency formatting.md) Number and Currency Formatting [Pluralization Rules](references/pluralization rules.md) Pluralization Rules [RTL (Right to Left) Language Support](references/rtl right to left language support.md) RTL (Right to Left) Language Support [Translation Management](references/translation management.md) Translation Management [Locale Detection](references/locale detection.md) Locale Detection [Server Side i18n](references/server side i18n.md) Server Side i18n Best Practices ✅ DO Extract all user facing strings to translation files Use ICU message format for complex messages Support pluralization correctly for each language Use locale aware date/time/number formatting Implement RTL support for Arabic, Hebrew, etc. Provide fallback language (usually English) Use namespaces to organize translations Test with pseudo localization (ääçćëńţś) Store locale preference (cookie, localStorage) Use professional translators for production Implement translation management workflow Support dynamic locale switching Use translation memory tools ❌ DON'T Hardcode user facing strings in code Concatenate translated strings Assume English grammar rules apply to all languages Use generic plural forms (one/many) for all languages Forget about text expansion (German is ~30% longer) Store dates/times in locale specific formats Use flags to represent languages (flag ≠ language) Translate technical terms without context Mix translation keys with UI strings Forget to translate alt text, titles, placeholders Assume left to right layout

internationalization-i18n