Add a new language/locale to the application. Involves Strapi admin config, Next.js i18n routing, and translation files.

Input Validation

Before proceeding, validate inputs:

•Locale code: must be valid ISO 639-1 (2 letters, lowercase, e.g. de, fr, sk). Reject uppercase or invalid codes.
•Locale name: capitalized, no special characters (e.g. German, French, Slovak).

If invalid format provided, ask user to correct before proceeding.

Inputs

Ask the user for:

•Locale code: ISO 639-1 code (e.g. de, fr, sk)
•Locale name: human-readable name (e.g. German, French, Slovak)

Steps

1. Create locale translation file

Copy apps/ui/locales/en.json to apps/ui/locales/{locale}.json.

The file structure must match en.json exactly — same keys, translated values. Initially copy as-is and mark values for translation.

Existing locales for reference: en.json, cs.json.

2. Update routing config

Edit apps/ui/src/lib/navigation.ts.

Add the new locale code to the locales array:

typescript

export const routing = defineRouting({
  locales: ["cs", "en", "{locale}"],
  defaultLocale: "en",
  localePrefix: "as-needed",
})

Keep the array sorted alphabetically.

3. Update i18n config (if needed)

The i18n config at apps/ui/src/lib/i18n.ts uses dynamic imports and automatically picks up new locale files:

typescript

messages: (
  await (locale === "en"
    ? import("../../locales/en.json")
    : import(`../../locales/${locale}.json`))
).default,

No changes needed unless you want HMR support for the new locale during development (currently only en has HMR via static import).

4. Manual steps (inform user)

After the automated steps complete, inform the user:

The translation file and routing config are set up. You need to manually:

•Enable locale in Strapi: Go to Settings > Internationalization > Add new locale > select {locale}

•Translate content: For each content type with i18n enabled, switch to the new locale in Strapi admin and translate

Notes

•The [locale] route segment in apps/ui/src/app/[locale]/ handles locale routing automatically via next-intl
•generateStaticParams in the root layout iterates routing.locales — new locale pages are generated automatically
•The localePrefix: "as-needed" setting means the default locale (en) has no prefix, all others get /{locale}/ prefix