# General Translation React SDKs (gt-react, gt-next, gt-react-native): App Router middleware
URL: https://generaltranslation.com/en-US/docs/react/nextjs/app-router-middleware.mdx
---
title: App Router middleware
description: How to configure General Translation locale routing for the Next.js App Router.
related:
links:
- /docs/react/nextjs/app-router-static-site-generation
- /docs/react/nextjs/registering-request-locales
- /docs/react/nextjs/cache-components
- /docs/react/nextjs/locale-alias-seo
---
Configure middleware, a `[locale]` root segment, and a request locale function so App Router requests resolve to the correct localized route.
## Configure the middleware [#middleware]
Create `proxy.ts` in your project root (`middleware.ts` on Next.js 15 and earlier):
```ts title="proxy.ts"
import { createNextMiddleware } from 'gt-next/middleware';
export default createNextMiddleware();
export const config = {
matcher: ['/((?!api|static|.*\\..*|_next).*)'],
};
```
The middleware detects the locale from the URL, cookie, browser headers, or default locale. It then redirects or rewrites the request to the matching localized route.
## Add the locale route [#locale-route]
Move your App Router pages under `app/[locale]`:
The route segment receives the locale selected by the middleware. See [`createNextMiddleware`](/docs/react/nextjs/reference/functions/create-next-middleware) for routing options and localized path configuration.
## Read the root locale [#root-locale]
Create `getLocale.ts` at your project root. `withGTConfig` detects this file automatically.
```ts title="./getLocale.ts"
import { locale } from 'next/root-params';
export default async function getLocale() {
return await locale();
}
```
The root parameter supplies the locale without reading request headers or cookies.
**Next.js 15.2–15.4:** `next/root-params` is available in Next.js 15.5 and
newer. On 15.2 through 15.4, import `unstable_rootParams` from `next/server`
and return `(await unstable_rootParams())?.locale` instead. Root params are
unavailable in any form before 15.2, so resolve the locale from the request
there.
## Reject unsupported locales [#validate-locales]
By default, an unsupported request locale produces a warning and falls back to `defaultLocale`. For strict locale-prefixed routes, validate the route parameter in `app/[locale]/layout.tsx` and call `notFound()`:
```tsx title="app/[locale]/layout.tsx"
import { isLocaleSupported } from 'gt-next';
import { notFound } from 'next/navigation';
export default async function LocaleLayout({
children,
params,
}: {
children: React.ReactNode;
params: Promise<{ locale: string }>;
}) {
const { locale } = await params;
if (!isLocaleSupported(locale)) {
notFound();
}
return (
{children}
);
}
```
[`isLocaleSupported`](/docs/react/nextjs/reference/functions/is-locale-supported) accepts configured locale aliases and narrows the value to `string`. The middleware does not automatically turn an unknown route segment into a 404.
## Next steps
- /docs/react/nextjs/app-router-static-site-generation
- /docs/react/nextjs/registering-request-locales
- /docs/react/nextjs/cache-components
- /docs/react/nextjs/locale-alias-seo