Internationalization (i18n)

Summary

Architecting an app so it can support multiple languages and locales — extracting all UI text into translation files instead of hardcoding strings.

• 1Extract hardcoded strings in a small project into a translation file (even just English).
• 2Add a second language and a language switcher using a library like `next-intl` or `react-i18next`.
• 3Learn to handle pluralization rules, which differ significantly across languages.