How to enable auto redirect when I want to use only domain based routing?

[siamahnaf]

Hello, I want to create a nextjs i18 app with subdomain based locale, like-

example.com //It is default locale, on default locale I want to use en
fr.example.com
de.example.com

I don't want to use prefix like-
fr.example.com/fr
de.example.com/de

That's why disable the locale prefix. Following is my code-

i18n.ts-

import { notFound } from "next/navigation";
import { getRequestConfig } from "next-intl/server";

const locales = ["en", "fr", "de"];

export default getRequestConfig(async ({ locale }) => {
    if (!locales.includes(locale as any)) notFound();
    return {
        messages: (await import(`../translate/${locale}.json`)).default
    };
});

middleware.ts-

import createMiddleware from "next-intl/middleware";

export default createMiddleware({
    locales: ["en", "fr", "de"],
    defaultLocale: "en",
    localePrefix: "never",
    domains: [
        {
            domain: "dev.localhost:3000",
            locales: ["en"],
            defaultLocale: "en"
        },
        {
            domain: "fr.dev.localhost:3000",
            locales: ["fr"],
            defaultLocale: "fr"
        },
        {
            domain: "de.dev.localhost:3000",
            locales: ["de"],
            defaultLocale: "de"
        }
    ]
});

export const config = {
    matcher: ['/((?!api|_next|.*\\..*).*)']
};

So, here you can see that, I use this localePrefix: "never",. Now it is not auto redirecting.

What I want?
I want to auto redirect to subdomain based routing without adding locale prefix. Suppose, detection locale is fr, but I am going to root domain example.com, it automatically should redirect to fr.example.com.

Again suppose, detection locale is en, but I am trying to go fr.example.com it should redirect to example.com, as here I want to use root domain for en locale.

Same as, if I previously switch locale to fr, next-intl is saving this onto cookie, then I try to go example.com, it should redirect to fr.example.com.

Could anyone please help me, I need to understand the whole things. Please say or give minimal example, how can I do that?

[amannn]

next-intl will use the defaultLocale of your domain as a fallback in your case, see the docs:

(4) As a fallback, the defaultLocale of the domain is used

Therefore no automatic redirect is done that would change the domain.

You can however compose the middleware and add additional redirects on top if you like before the next-intl middleware handles the request.

[Matt-Cain]

Hi 👋 , I am also running into a similar issue with auto redirects to subdomains not working as expected.

Expected:

• When I navigate to local.app.com with Accept-Language: pt-BR;q=0.9
• I should be redirect to pt.local.app.com

Actually:

• When I navigate to local.app.com with Accept-Language: pt-BR;q=0.9
• I am not redirected, but stay on local.app.com
• However, the content on the page shows the correct language

import { defineRouting } from 'next-intl/routing';

export const routing = defineRouting({
  defaultLocale: 'en-US',
  domains: [
    {
      defaultLocale: 'en-US',
      domain: 'en.local.app.com',
      locales: ['en-US'],
    },
    {
      defaultLocale: 'pt-BR',
      domain: 'pt.local.app.com',
      locales: ['pt-BR'],
    },
    {
      defaultLocale: 'es',
      domain: 'es.local.app.com',
      locales: ['es'],
    },
  ],
  localePrefix: { mode: 'never' },
  locales: ['en-US', 'pt-BR', 'es'],
});

Important to note: When I set localePrefix to { mode: 'always' }, I get redirected properly, albeit prefix-based routing

    "next": "15.3.1",
    "next-intl": "^4.1.0",
    "react": "^19.0.0",