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App Router

Next.js App Router Internationalization (i18n)

The Next.js App Router introduces support for React Server Components (opens in a new tab) and unlocks many benefits when handling internationalization on the server side.

Getting started

If you haven't done so already, create a Next.js app that uses the App Router (opens in a new tab).

next-intl integrates with the App Router, by using a [locale] dynamic segment (opens in a new tab) so that we can use this segment to provide content in different languages (e.g. /en, /en/about, etc.).

Let's get started!

Run npm install next-intl and create the following file structure:

├── messages (1)
│   ├── en.json
│   └── ...
├── next.config.js (2)
└── src
    ├── i18n.ts (3)
    ├── middleware.ts (4)
    └── app
        └── [locale]
            ├── layout.tsx (5)
            └── page.tsx (6)

Now, set up the files as follows:

messages/en.json

Messages can be provided locally or loaded from a remote data source (e.g. a translation management system). Use whatever suits your workflow best.

The simplest option is to add JSON files in your project based on locales, e.g. en.json.

messages/en.json
{
  "Index": {
    "title": "Hello world!"
  }
}

next.config.js

Now, set up the plugin which creates an alias to import your i18n configuration (specified in the next step) into Server Components.

next.config.js
const withNextIntl = require('next-intl/plugin')();
 
module.exports = withNextIntl({
  // Other Next.js configuration ...
});

src/i18n.ts

next-intl creates a configuration once per request. Here you can provide messages and other options depending on the locale of the user.

src/i18n.ts
import {getRequestConfig} from 'next-intl/server';
 
export default getRequestConfig(async ({locale}) => ({
  messages: (await import(`../messages/${locale}.json`)).default
}));
Can I move this file somewhere else?

This file is supported out-of-the-box both in the src folder as well as in the project root with the extensions .ts, .tsx, .js and .jsx.

If you prefer to move this file somewhere else, you can provide an optional path to the plugin:

next.config.js
const withNextIntl = require('next-intl/plugin')(
  // Specify a custom path here
  './somewhere/else/i18n.ts'
);
 
module.exports = withNextIntl({
  // Other Next.js configuration ...
});

middleware.ts

The middleware matches a locale for the request and handles redirects and rewrites accordingly.

middleware.ts
import createMiddleware from 'next-intl/middleware';
 
export default createMiddleware({
  // A list of all locales that are supported
  locales: ['en', 'de'],
 
  // Used when no locale matches
  defaultLocale: 'en'
});
 
export const config = {
  // Match only internationalized pathnames
  matcher: ['/', '/(de|en)/:path*']
};

app/[locale]/layout.tsx

The locale that was matched by the middleware is available via the locale param and can be used to configure the document language.

app/[locale]/layout.tsx
import {notFound} from 'next/navigation';
 
// Can be imported from a shared config
const locales = ['en', 'de'];
 
export default function LocaleLayout({children, params: {locale}}) {
  // Validate that the incoming `locale` parameter is valid
  if (!locales.includes(locale as any)) notFound();
 
  return (
    <html lang={locale}>
      <body>{children}</body>
    </html>
  );
}

app/[locale]/page.tsx

Use translations in your page components or anywhere else!

app/[locale]/page.tsx
import {useTranslations} from 'next-intl';
 
export default function Index() {
  const t = useTranslations('Index');
  return <h1>{t('title')}</h1>;
}

That's all it takes!

💡

Next steps:

Static rendering

By using APIs like useTranslations from next-intl in Server Components, your pages will currently opt into dynamic rendering (opens in a new tab). This is a limitation that we aim to remove in the future, but as a stopgap solution, next-intl provides a temporary API that can be used to enable static rendering:

Add generateStaticParams to app/[locale]/layout.tsx

Since we use a dynamic route segment for the [locale] param, we need to provide all possible values via generateStaticParams (opens in a new tab) to Next.js, so the routes can be rendered at build time.

app/[locale]/layout.tsx
const locales = ['en', 'de'];
 
export function generateStaticParams() {
  return locales.map((locale) => ({locale}));
}

Add unstable_setRequestLocale to all layouts and pages

next-intl provides a temporary API that can be used to distribute the locale that is received via params in a layout or page for usage in all Server Components that are rendered as part of the request.

app/[locale]/layout.tsx
import {unstable_setRequestLocale} from 'next-intl/server';
 
const locales = ['en', 'de'];
 
export default async function LocaleLayout({
  children,
  params: {locale}
}) {
  // Validate that the incoming `locale` parameter is valid
  if (!locales.includes(locale as any)) notFound();
 
  unstable_setRequestLocale(locale);
 
  return (
    // ...
  );
}
app/[locale]/page.tsx
import {unstable_setRequestLocale} from 'next-intl/server';
import {locales} from '..';
 
export default function IndexPage({
  params: {locale}
}) {
  unstable_setRequestLocale(locale);
 
  // Once the request locale is set, you
  // can call hooks from `next-intl`
  const t = useTranslations('IndexPage');
 
  return (
    // ...
  );
}

Important: unstable_setRequestLocale needs to be called after the locale is validated, but before you call any hooks from next-intl. Otherwise, you'll get an error when trying to prerender the page.

Note that Next.js can render layouts and pages indepently. This means that e.g. when you navigate from /settings/profile to /settings/privacy, the /settings segment might not re-render as part of the request. Due to this, it's important that unstable_setRequestLocale is called not only in the parent settings/layout.tsx, but also in the individual pages profile/page.tsx and privacy/page.tsx.

What does "unstable" mean?

unstable_setRequestLocale is meant to be used as a stopgap solution and we aim to remove it in the future in case Next.js adds an API to access parts of the URL (opens in a new tab). If that's the case, you'll get a deprecation notice in a minor version and the API will be removed as part of a major version.

That being said, the API is expected to work reliably if you're cautious to apply it in all relevant places.

How does unstable_setRequestLocale work?

next-intl uses cache() (opens in a new tab) to create a mutable store that holds the current locale. By calling unstable_setRequestLocale, the current locale will be written to the store, making it available to all APIs that require the locale.

Note that the store is scoped to a request and therefore doesn't affect other requests that might be handled in parallel while a given request resolves asynchronously.

Why is this API necessary?

Next.js currently doesn't provide an API to read route params like locale at arbitrary places in Server Components. The locale is fundamental to all APIs provided by next-intl, therefore passing this as a prop throughout the tree doesn't stand out as particularly ergnomic.

Due to this, next-intl uses its middleware to attach an x-next-intl-locale header to the incoming request, holding the negotiated locale as a value. This technique allows the locale to be read at arbitrary places via headers().get('x-next-intl-locale').

However, the usage of headers opts the route into dynamic rendering.

By using unstable_setRequestLocale, you can provide the locale that is received in layouts and pages via params to next-intl. By doing this, all APIs from next-intl can now read from this value instead of the header, enabling static rendering.

Use the locale param in metadata

In addition to the rendering of your pages, also page metadata needs to qualify for static rendering.

To achieve this, you can forward the locale that you receive from Next.js via params to the awaitable functions from next-intl.

page.tsx
import {getTranslations} from 'next-intl/server';
 
export async function generateMetadata({params: {locale}}) {
  const t = await getTranslations({locale, namespace: 'Metadata'});
 
  return {
    title: t('title')
  };
}
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