Next.js middleware for i18n routing
The middleware handles redirects and rewrites based on the detected user locale.
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*']
};
In addition to handling i18n routing, the middleware sets the link
header (opens in a new tab) to inform search engines that your content is available in different languages.
Strategies
There are two strategies for detecting the locale:
Once a locale is detected, it will be saved in the NEXT_LOCALE
cookie.
Strategy 1: Prefix-based routing (default)
Since your pages are nested within a [locale]
folder, all routes are by default prefixed with one of your supported locales (e.g. /en/about
).
Locale detection
The locale is detected based on these priorities:
- A locale prefix is present in the pathname (e.g.
/en/about
) - A cookie is present that contains a previously detected locale
- A locale can be matched based on the
accept-language
header (opens in a new tab) - As a last resort, the
defaultLocale
is used
To change the locale, users can visit a prefixed route. This will take precedence over a previously matched locale that is saved in a cookie or the accept-language
header and will update the previous cookie value.
Example workflow:
- A user requests
/
and based on theaccept-language
header, theen
locale is matched. - The
en
locale is saved in a cookie and the user is redirected to/en
. - The app renders
<Link locale="de" href="/">Switch to German</Link>
to allow the user to change the locale tode
. - When the user clicks on the link, a request to
/de
is initiated. - The middleware will update the cookie value to
de
.
You can optionally remove the locale prefix in pathnames by changing the
localePrefix
setting.
Strategy 2: Domain-based routing
If you want to serve your localized content based on different domains, you can provide a list of mappings between domains and locales to the middleware.
Examples:
us.example.com/en
ca.example.com/en
ca.example.com/fr
import createMiddleware from 'next-intl/middleware';
export default createMiddleware({
// All locales across all domains
locales: ['en', 'fr'],
// Used when no domain matches (e.g. on localhost)
defaultLocale: 'en',
domains: [
{
domain: 'us.example.com',
defaultLocale: 'en',
// Optionally restrict the locales managed by this domain. If this
// domain receives requests for another locale (e.g. us.example.com/fr),
// then the middleware will redirect to a domain that supports it.
locales: ['en']
},
{
domain: 'ca.example.com',
defaultLocale: 'en'
// If there are no `locales` specified on a domain,
// all global locales will be supported here.
}
]
});
You can optionally remove the locale prefix in pathnames by changing the
localePrefix
setting.
Locale detection
To match the request against the available domains, the host is read from the x-forwarded-host
header, with a fallback to host
.
The locale is detected based on these priorities:
- A locale prefix is present in the pathname and the domain supports it (e.g.
ca.example.com/fr
) - If the host of the request is configured in
domains
, thedefaultLocale
of the domain is used - As a fallback, the locale detection of prefix-based routing applies
Since the middleware is aware of all your domains, the domain will automatically be switched when the user requests to change the locale.
Example workflow:
- The user requests
us.example.com
and based on thedefaultLocale
of this domain, theen
locale is matched. - The app renders
<Link locale="fr" href="/">Switch to French</Link>
to allow the user to change the locale tofr
. - When the link is clicked, a request to
us.example.com/fr
is initiated. - The middleware recognizes that the user wants to switch to another domain and responds with a redirect to
ca.example.com/fr
.
How is the best matching domain for a given locale detected?
The bestmatching domain is detected based on these priorities:
- Stay on the current domain if the locale is supported here
- Use an alternative domain where the locale is configured as the
defaultLocale
- Use an alternative domain where the available
locales
are restricted and the locale is supported - Stay on the current domain if it supports all locales
- Use an alternative domain that supports all locales
Further configuration
Locale prefix
If you're using the navigation APIs from next-intl
, you want to make sure your localePrefix
setting matches your middleware configuration.
Always use a locale prefix
By default, pathnames always start with the locale (e.g. /en/about
).
import createMiddleware from 'next-intl/middleware';
export default createMiddleware({
// ... other config
localePrefix: 'always' // This is the default
});
How can I redirect unprefixed pathnames?
If you want to redirect unprefixed pathnames like /about
to a prefixed alternative like /en/about
, you can adjust your middleware matcher to match unprefixed pathnames too.
Don't use a locale prefix for the default locale
If you don't want to include a locale prefix for the default locale, but only for non-default locales, you can configure the middleware accordingly.
import createMiddleware from 'next-intl/middleware';
export default createMiddleware({
// ... other config
localePrefix: 'as-needed'
});
In this case, requests where the locale prefix matches the default locale will be redirected (e.g. /en/about
to /about
). This will affect both prefix-based as well as domain-based routing.
Important: If you use this strategy, you should make sure that your matcher detects unprefixed pathnames.
If you use the Link
component, the initial
render will point to the prefixed version but will be patched immediately on
the client once the component detects that the default locale has rendered.
The prefixed version is still valid, but SEO tools might report a hint that
the link points to a redirect.
Never use a locale prefix
If you're building an app behind an authentication layer, where there is no need for SEO, or you're using domain-based routing and you support only a single locale per domain, you can configure the middleware to never show a locale prefix in the URL.
import createMiddleware from 'next-intl/middleware';
export default createMiddleware({
// ... other config
localePrefix: 'never'
});
In this case, requests for all locales will be rewritten to have the locale only prefixed internally. You still need to place all your pages inside a [locale]
folder for the routes to be able to receive the locale
param.
Important notes:
- If you use this strategy, you should make sure that your matcher detects unprefixed pathnames.
- If you don't use domain-based routing, the cookie is now the source of truth for determining the locale in the middleware. Make sure that your hosting solution reliably returns the
set-cookie
header from the middleware (e.g. Vercel and Cloudflare are known to potentially strip this header (opens in a new tab) for cacheable requests). - Alternate links are disabled in this mode since there might not be distinct URLs per locale.
Disable locale detection
If you want to rely entirely on the URL to resolve the locale, you can disable locale detection based on the accept-language
header and a potentially existing cookie value from a previous visit.
import createMiddleware from 'next-intl/middleware';
export default createMiddleware({
// ... other config
localeDetection: false
});
In this case, only the locale prefix and a potentially matching domain are used to determine the locale.
Note that by setting this option, the middleware will no longer return a set-cookie
response header, which can be beneficial for CDN caching (see e.g. the Cloudflare Cache rules for set-cookie
(opens in a new tab)).
Disable alternate links
The middleware automatically sets the link
header (opens in a new tab) to inform search engines that your content is available in different languages. Note that this automatically integrates with your routing strategy and will generate the correct links based on your configuration.
If you prefer to include these links yourself, you can opt-out of this behavior.
import createMiddleware from 'next-intl/middleware';
export default createMiddleware({
// ... other config
alternateLinks: false // Defaults to `true`
});
Can I customize the alternate links?
The alternate links can either be turned off or on, depending on the alternateLinks
option.
If you need to customize the alternate links, you can either turn them off and provide your own implementation, or if you only need to make minor adaptions, you can compose the middleware and add your custom logic after the middleware has run:
import createIntlMiddleware from 'next-intl/middleware';
import LinkHeader from 'http-link-header';
import {NextRequest} from 'next/server';
const handleI18nRouting = createIntlMiddleware(/* ... */);
export default async function middleware(request: NextRequest) {
const response = handleI18nRouting(request);
// Example: Remove the `x-default` entry
const link = LinkHeader.parse(response.headers.get('link'));
link.refs = link.refs.filter((entry) => entry.hreflang !== 'x-default');
response.headers.set('link', link.toString());
return response;
}
Localizing pathnames
Many apps choose to localize pathnames, especially when search engine optimization is relevant, e.g.:
/en/about
/de/ueber-uns
Since you want to define these routes only once internally, you can use the next-intl
middleware to rewrite (opens in a new tab) such incoming requests to shared pathnames.
import createMiddleware from 'next-intl/middleware';
export default createMiddleware({
defaultLocale: 'en',
locales: ['en', 'de'],
// The `pathnames` object holds pairs of internal and
// external paths. Based on the locale, the external
// paths are rewritten to the shared, internal ones.
pathnames: {
// If all locales use the same pathname, a single
// external path can be used for all locales.
'/': '/',
'/blog': '/blog',
// If locales use different paths, you can
// specify each external path per locale.
'/about': {
en: '/about',
de: '/ueber-uns'
},
// Dynamic params are supported via square brackets
'/news/[articleSlug]-[articleId]': {
en: '/news/[articleSlug]-[articleId]',
de: '/neuigkeiten/[articleSlug]-[articleId]'
},
// Also (optional) catch-all segments are supported
'/categories/[...slug]': {
en: '/categories/[...slug]',
de: '/kategorien/[...slug]'
}
}
});
If you have pathname localization set up in the middleware, you likely want to use the localized navigation APIs in your components.
Matcher config
The middleware is intended to only run on pages, not on arbitrary files that you serve independently of the user locale (e.g. /favicon.ico
).
Because of this, the following config is generally recommended:
export const config = {
// Match only internationalized pathnames
matcher: ['/', '/(de|en)/:path*']
};
This enables:
- A redirect at
/
to a suitable locale - Internationalization of all pathnames starting with a locale (e.g.
/en/about
)
Pathnames without a locale prefix
There are two use cases where you might want to match pathnames without a locale prefix:
- You're using a config for
localePrefix
other thanalways
- You want to implement redirects that add a locale for unprefixed pathnames (e.g.
/about
→/en/about
)
For these cases, the middleware should run on requests for pathnames without a locale prefix as well.
A popular strategy is to match all routes that don't start with certain segments (e.g. /_next
) and also none that include a dot (.
) since these typically indicate static files. However, if you have some routes where a dot is expected (e.g. /users/jane.doe
), you should explicitly provide a matcher for these.
export const config = {
// Matcher entries are linked with a logical "or", therefore
// if one of them matches, the middleware will be invoked.
matcher: [
// Match all pathnames except for
// - … if they start with `/api`, `/_next` or `/_vercel`
// - … the ones containing a dot (e.g. `favicon.ico`)
'/((?!api|_next|_vercel|.*\\..*).*)',
// However, match all pathnames within `/users`, optionally with a locale prefix
'/([\\w-]+)?/users/(.+)'
]
};
Note that some third-party providers like Vercel Analytics (opens in a new tab) and umami (opens in a new tab) typically use internal endpoints that are then rewritten to an external URL (e.g. /_vercel/insights/view
). Make sure to exclude such requests from your middleware matcher so they aren't accidentally rewritten.
Base path
The next-intl
middleware as well as the navigation APIs will automatically pick up a basePath
(opens in a new tab) that you might have configured in your next.config.js
.
Note however that you should make sure that your middleware matcher
matches the root of your base path:
// ...
export const config = {
matcher: [
'/' // Make sure the root is matched
// ... other matcher config
]
};
See also: vercel/next.js#47085
(opens in a new tab)
Composing other middlewares
By calling createMiddleware
, you'll receive a function of the following type:
middleware(request: NextRequest): NextResponse
If you need to incorporate additional behavior, you can either modify the request before the next-intl
middleware receives it, or modify the response that is returned.
import createIntlMiddleware from 'next-intl/middleware';
import {NextRequest} from 'next/server';
export default async function middleware(request: NextRequest) {
// Step 1: Use the incoming request (example)
const defaultLocale = request.headers.get('x-your-custom-locale') || 'en';
// Step 2: Create and call the next-intl middleware (example)
const handleI18nRouting = createIntlMiddleware({
locales: ['en', 'de'],
defaultLocale
});
const response = handleI18nRouting(request);
// Step 3: Alter the response (example)
response.headers.set('x-your-custom-locale', defaultLocale);
return response;
}
export const config = {
// Match only internationalized pathnames
matcher: ['/', '/(de|en)/:path*']
};
Example: Additional rewrites
If you need to handle rewrites apart from the ones provided by next-intl
, you can adjust the pathname
of the request
before invoking the next-intl
middleware (based on "A/B Testing with Cookies" by Vercel (opens in a new tab)).
This example rewrites requests for /[locale]/profile
to /[locale]/profile/new
if a special cookie is set.
import createIntlMiddleware from 'next-intl/middleware';
import {NextRequest} from 'next/server';
export default async function middleware(request: NextRequest) {
const [, locale, ...segments] = request.nextUrl.pathname.split('/');
if (locale != null && segments.join('/') === 'profile') {
const usesNewProfile =
(request.cookies.get('NEW_PROFILE')?.value || 'false') === 'true';
if (usesNewProfile) {
request.nextUrl.pathname = `/${locale}/profile/new`;
}
}
const handleI18nRouting = createIntlMiddleware({
locales: ['en', 'de'],
defaultLocale: 'en'
});
const response = handleI18nRouting(request);
return response;
}
export const config = {
matcher: ['/', '/(de|en)/:path*']
};
Note that if you use a localePrefix
other than always
, you need to adapt the handling appropriately to handle unprefixed pathnames too.
Example: Integrating with Clerk
@clerk/nextjs
(opens in a new tab) provides a middleware that can be integrated with next-intl
by using the beforeAuth
hook (opens in a new tab). By doing this, the middleware from next-intl
will run first, potentially redirect or rewrite incoming requests, followed by the middleware from @clerk/next
acting on the response.
import {authMiddleware} from '@clerk/nextjs';
import createMiddleware from 'next-intl/middleware';
const intlMiddleware = createMiddleware({
locales: ['en', 'de'],
defaultLocale: 'en'
});
export default authMiddleware({
beforeAuth(request) {
return intlMiddleware(request);
},
// Ensure that locale-specific sign in pages are public
publicRoutes: ['/:locale', '/:locale/sign-in']
});
export const config = {
// Match only internationalized pathnames
matcher: ['/', '/(de|en)/:path*']
};
Example: Integrating with Supabase Authentication
@supabase/auth-helpers-nextjs
(opens in a new tab) exports createMiddlewareClient
that accepts a req
and res
object. We can pass the incoming req
and the res
created with createIntlMiddleware
to it.
import {createMiddlewareClient} from '@supabase/auth-helpers-nextjs';
import createIntlMiddleware from 'next-intl/middleware';
import type {NextRequest} from 'next/server';
import type {Database} from '@/lib/database.types';
export default async function middleware(req: NextRequest) {
const handleI18nRouting = createIntlMiddleware({
locales: ['en', 'de'],
defaultLocale: 'en'
});
const res = handleI18nRouting(req);
const supabase = createMiddlewareClient<Database>({req, res});
await supabase.auth.getSession();
return res;
}
export const config = {
matcher: ['/', '/(de|en)/:path*']
};
Example: Integrating with Auth.js (aka NextAuth.js)
The Next.js middleware of Auth.js (opens in a new tab) requires an integration with their control flow to be compatible with other middlewares. The success callback (opens in a new tab) can be used to run the next-intl
middleware on authorized pages. However, public pages need to be treated separately.
For pathnames specified in the pages
object (opens in a new tab) (e.g. signIn
), Auth.js will skip the entire middleware and not run the success callback. Therefore, we have to detect these pages before running the Auth.js middleware and only run the next-intl
middleware in this case.
import {withAuth} from 'next-auth/middleware';
import createIntlMiddleware from 'next-intl/middleware';
import {NextRequest} from 'next/server';
const locales = ['en', 'de'];
const publicPages = ['/', '/login'];
const intlMiddleware = createIntlMiddleware({
locales,
localePrefix: 'as-needed',
defaultLocale: 'en'
});
const authMiddleware = withAuth(
// Note that this callback is only invoked if
// the `authorized` callback has returned `true`
// and not for pages listed in `pages`.
function onSuccess(req) {
return intlMiddleware(req);
},
{
callbacks: {
authorized: ({token}) => token != null
},
pages: {
signIn: '/login'
}
}
);
export default function middleware(req: NextRequest) {
const publicPathnameRegex = RegExp(
`^(/(${locales.join('|')}))?(${publicPages
.flatMap((p) => (p === '/' ? ['', '/'] : p))
.join('|')})/?$`,
'i'
);
const isPublicPage = publicPathnameRegex.test(req.nextUrl.pathname);
if (isPublicPage) {
return intlMiddleware(req);
} else {
return (authMiddleware as any)(req);
}
}
export const config = {
matcher: ['/((?!api|_next|.*\\..*).*)']
};
There's a working example that combines next-intl
with Auth.js on GitHub.
Usage without middleware (static export)
If you're using the static export feature from Next.js (opens in a new tab) (output: 'export'
), the middleware will not run. You can use prefix-based routing nontheless to internationalize your app, but a few tradeoffs apply.
Static export limitations:
- There's no default locale that can be used without a prefix (same as
localePrefix: 'always'
) - The locale can't be negotiated at runtime (same as
localeDetection: false
) - You can't use pathname localization
- This requires static rendering
- You need to add a redirect for the root of the app
import {redirect} from 'next/navigation';
// Redirect the user to the default locale when `/` is requested
export default function RootPage() {
redirect('/en');
}
You can explore a working demo by building the Next.js App Router example after enabling the static export:
module.exports = {
output: 'export'
};
Troubleshooting
"Unable to find next-intl
locale because the middleware didn't run on this request."
This can happen either because:
- The middleware is not set up.
- The middleware is set up in the wrong file (e.g. you're using the
src
folder, butmiddleware.ts
was added in the root folder). - The middleware matcher didn't match a request, but you're using APIs from
next-intl
in a component. - You're attempting to implement static rendering via
force-static
(opens in a new tab).
To recover from this error, please make sure that:
- You've set up the middleware.
- You're using APIs from
next-intl
(including the navigation APIs) exclusively within thelocale
segment. - Your middleware matcher matches all routes of your application, including dynamic segments with potentially unexpected characters like dots (e.g.
/users/jane.doe
). - If you're using
localePrefix: 'as-needed'
, thelocale
segment effectively acts like a catch-all for all unknown routes. You should make sure thatparams.locale
is validated before it's used by any APIs fromnext-intl
. - To implement static rendering, make sure to provide a static locale to
next-intl
instead of usingforce-static
.
Note that next-intl
will print this warning only during development and will invoke the notFound()
function to abort the render. You should consider adding a not-found
page due to this.