next-intl-add-language

This is a guide to add a new language to a Next.js project using next-intl for internationalization.

Input validation (required): Before constructing any file path or inserting the language code into TypeScript source files, verify the supplied language code matches BCP 47 format: characters must be exclusively from [a-zA-Z0-9-], with no path separators (/, \), no quotes, no semicolons, and no whitespace. Reject and abort if the input does not match. Do not proceed with any file operation until this check passes.

Preflight path check (required): Before making any changes, verify that the following paths exist in the project:

• ./messages/en.json
• src/components/language-toggle.tsx
• src/i18n/routing.ts
• src/middleware.ts

If any path is missing or differs, surface the discrepancy to the user and request confirmation of the correct paths before proceeding. Do not guess or create missing directories silently.

• For i18n, the application uses next-intl.
• All translations are in the directory ./messages.
• The UI component is src/components/language-toggle.tsx.
• Routing and middleware configuration are handled in:
  • src/i18n/routing.ts
  • src/middleware.ts

When adding a new language:

• Translate all the content of messages/en.json to the new language. The goal is to have all the JSON entries in the new language for a complete translation.
• Add the path in routing.ts and middleware.ts.
• Add the language to language-toggle.tsx.