Server Actions, Metadata & Route Handlers

There are a few places in Next.js apps where you can apply internationalization outside of React components:

1. Server Actions (opens in a new tab)
2. Metadata API (opens in a new tab)
3. Open Graph images (opens in a new tab)
4. Manifest (opens in a new tab)
5. Sitemap (opens in a new tab)
6. Route Handlers (opens in a new tab)

next-intl/server provides a set of awaitable functions that can be used in these cases.

Server Actions

Server Actions (opens in a new tab) provide a mechanism to execute server-side code that is invoked by the client. In case you're returning user-facing messages, you can use next-intl to localize them based on the user's locale.

import {getTranslations} from 'next-intl/server';
 
async function loginAction(data: FormData) {
  'use server';
 
  const t = await getTranslations('LoginForm');
  const areCredentialsValid = /* ... */;
  if (!areCredentialsValid) {
    return {error: t('invalidCredentials')};
  }
}

Note that when you're displaying messages generated in Server Actions to the user, you should consider the case if the user can switch the locale while the message is displayed to ensure that the UI is localized consistently. If you're using a [locale] segment as part of your routing strategy then this is handled automatically. If you're not, you might want to clear the message manually, e.g. by resetting the state (opens in a new tab) of the respective component via key={locale}.

import {getTranslations} from 'next-intl/server';
import {loginUser} from '@/services/session';
import {isEqual} from 'lodash';
import {z} from 'zod';
 
const loginFormSchema = z.object({
  email: z.string().email(),
  password: z.string().min(1)
});
 
// ...
 
async function loginAction(data: FormData) {
  'use server';
 
  const t = await getTranslations('LoginForm');
  const values = Object.fromEntries(data);
 
  const result = await loginFormSchema
    .refine(async (credentials) => loginUser(credentials), {
      message: t('invalidCredentials')
    })
    .safeParseAsync(values, {
      errorMap(issue, ctx) {
        let message;
 
        if (isEqual(issue.path, ['email'])) {
          message = t('invalidEmail');
        } else if (isEqual(issue.path, ['password'])) {
          message = t('invalidPassword');
        }
 
        return {message: message || ctx.defaultError};
      }
    });
 
  // ...
}

Metadata API

To internationalize metadata like the page title, you can use functionality from next-intl in the generateMetadata (opens in a new tab) function that can be exported from pages and layouts.

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

Open Graph images

If you're programmatically generating Open Graph images (opens in a new tab), you can apply internationalization by calling functions from next-intl in the exported function:

import {ImageResponse} from 'next/og';
import {getTranslations} from 'next-intl/server';
 
export default async function OpenGraphImage({params: {locale}}) {
  const t = await getTranslations({locale, namespace: 'OpenGraphImage'});
  return new ImageResponse(<div style={{fontSize: 128}}>{t('title')}</div>);
}

Manifest

Since the manifest file (opens in a new tab) needs to be placed in the root of the app folder (outside the [locale] dynamic segment), you need to provide a locale explicitly since next-intl can't infer it from the pathname:

import {MetadataRoute} from 'next';
import {getTranslations} from 'next-intl/server';
 
export default async function manifest(): Promise<MetadataRoute.Manifest> {
  // Pick a locale that is representative of the app
  const locale = 'en';
 
  const t = await getTranslations({
    namespace: 'Manifest',
    locale
  });
 
  return {
    name: t('name'),
    start_url: '/',
    theme_color: '#101E33'
  };
}

Sitemap

If you're using a sitemap to inform search engines about all pages of your site, you can attach locale-specific alternate entries (opens in a new tab) to every URL in the sitemap to indicate that a particular page is available in multiple languages or regions.

Note that by default, next-intl returns the link response header to instruct search engines that a page is available in multiple languages. While this sufficiently links localized pages for search engines, you may choose to provide this information in a sitemap in case you have more specific requirements.

Next.js supports providing alternate URLs per language via the alternates entry (opens in a new tab) as of version 14.2. You can use your default locale for the main URL and provide alternate URLs based on all locales that your app supports. Keep in mind that also the default locale should be included in the alternates object.

import {MetadataRoute} from 'next';
 
// Can be imported from shared config
const defaultLocale = 'en' as const;
const locales = ['en', 'de'] as const;
 
// Adapt this as necessary
const pathnames = ['/', '/about'];
const host = 'https://acme.com';
 
export default function sitemap(): MetadataRoute.Sitemap {
  function getUrl(pathname: string, locale: string) {
    return `${host}/${locale}${pathname === '/' ? '' : pathname}`;
  }
 
  return pathnames.map((pathname) => ({
    url: getUrl(pathname, defaultLocale),
    lastModified: new Date(),
    alternates: {
      languages: Object.fromEntries(
        locales.map((locale) => [locale, getUrl(pathname, locale)])
      )
    }
  }));
}

Route Handlers

You can use next-intl in Route Handlers (opens in a new tab) too. The locale can either be received from a search param, a layout segment or by parsing the accept-language header of the request.

import {NextResponse} from 'next/server';
import {getTranslations} from 'next-intl/server';
 
export async function GET(request) {
  // Example: Receive the `locale` via a search param
  const {searchParams} = new URL(request.url);
  const locale = searchParams.get('locale');
 
  const t = await getTranslations({locale, namespace: 'Hello'});
  return NextResponse.json({title: t('title')});
}