i18next/next-i18next v16.0.0

on GitHub

BREAKING CHANGES

• Import paths changed for Pages Router: next-i18next → next-i18next/pages, next-i18next/serverSideTranslations → next-i18next/pages/serverSideTranslations
• Root export is now App Router: The default next-i18next import now exports App Router utilities (defineConfig, normalizeConfig, I18nConfig). Pages Router users must update to next-i18next/pages.
• Removed i18next-fs-backend dependency: Pages Router server-side loading now uses i18next-resources-to-backend with fs.readFileSync internally. No change needed for users — the behavior is identical.

New Features

• App Router support — first-class support for Next.js App Router with Server Components and Client Components
  • getT(ns?, options?) — async translation function for Server Components, layouts, and generateMetadata. Returns namespace-typed { t, i18n, lng }.
  • useT(ns?, options?) — translation hook for Client Components. Reads language from [lng] or [locale] URL params automatically.
  • I18nProvider — client-side provider for hydrating server-loaded translations. Supports custom backends via use prop.
  • initServerI18next(config) — one-time server configuration setup
  • getResources(i18n, namespaces?) — extract loaded resources for client hydration
  • generateI18nStaticParams() — helper for generateStaticParams
• Proxy support (Next.js 16+) — createProxy() from next-i18next/proxy for the new proxy.ts file convention. createMiddleware() from next-i18next/middleware remains available for Next.js 14/15.
  • Edge-safe language detection (cookie → Accept-Language → fallback)
  • Locale-in-path routing with automatic redirects
  • Custom header for Server Component language detection
• basePath option — scope the proxy to a URL prefix (e.g., /app-router) for mixed App Router + Pages Router setups
• No-locale-path mode — localeInPath: false for cookie-based language without URL prefixes. Use useChangeLanguage() hook for language switching.
• defineConfig() — type-safe configuration helper
• Custom backend support — pass any i18next backend plugin (http-backend, locize-backend, chained-backend) via the use config option. The default resource loader is skipped automatically when a custom backend is provided.
• resourceLoader option — custom async loader function (lng, ns) => Promise<object> for dynamic imports or custom loading logic
• Server-side singleton caching — translations loaded once and reused across requests. Custom backends benefit from this — no re-fetching per request.
• nonExplicitSupportedLngs — match 'en' to 'en-US' etc. in language detection

Pages Router

• All existing v15 APIs preserved under next-i18next/pages and next-i18next/pages/serverSideTranslations
• appWithTranslation, useTranslation, Trans, serverSideTranslations — unchanged behavior
• Defensive .filter(Boolean) on config.use arrays to handle CJS/ESM interop edge cases with Turbopack