SSR output includes “/en” prefix for default locale despite localePrefix: "as-needed"

[iProgrammerDmytro]

Description

We’re using Next-Intl in our Next.js 14.2.13 project to support multiple locales. Our default locale is English (en), and in routing.ts we set:

export const routing = defineRouting({
  locales: ["en", "es", "de", "fr", "nl"],
  defaultLocale: "en",
  localePrefix: "as-needed",
  // ... pathnames
});

Expected behavior:

• The default locale (en) should not show the "/en" prefix in server‐rendered HTML (SSR).
• When browsing in the browser’s DevTools Elements tab, we indeed see links like href="/book-a-demo" for English.

Actual behavior:
• In “View Page Source” (or if we do curl https://www.example.com), the SSR HTML has href="/en/book-a-demo" for English pages.
• This means search engine crawlers (Ahrefs, etc.) detect "/en/..." and flag them as redirects.
• After hydration on the client, the final DOM changes them to "/book-a-demo", but the raw SSR output still has "/en/".

We’ve verified there are no explicit references to "/en/" in our code (we searched the repo). Our localePrefix: "as-needed" is supposed to hide the default-locale prefix. However, SSR is still injecting "/en/".

Verifications

• I've verified that the problem I'm experiencing isn't covered in the docs.
• I've searched for similar, existing issues on GitHub and Stack Overflow.
• I've compared my app to a working example to look for differences.

Mandatory reproduction URL

Unfortunately, we don’t currently have a public minimal repo reproducing this. But here are some relevant code snippets from our real project. We can try to create a smaller reproduction if needed

Reproduction description

1. Install Next.js ^14.2.13 and Next-Intl ^3.19.4.
2. Configure routing.ts:

import { defineRouting } from "next-intl/routing";
import { createLocalizedPathnamesNavigation } from "next-intl/navigation";

export const routing = defineRouting({
  locales: ["en", "es", "de", "fr", "nl"],
  defaultLocale: "en",
  localePrefix: "as-needed",
  pathnames: {
    "/": "/",
    "/book-a-demo": {
      en: "/book-a-demo",
      es: "/reservar-una-demostracion",
      // ...
    },
    // etc.
  },
});

export const { Link, usePathname, useRouter } =
  createLocalizedPathnamesNavigation(routing);

3. Use Next-Intl’s middleware in middleware.ts:

import createMiddleware from "next-intl/middleware";
import { routing } from "./i18n/routing";

export default createMiddleware(routing, {
  localeDetection: false,
  alternateLinks: false,
});

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

4. SSR output (via “View Page Source” or curl):

<a href="/en/book-a-demo" class="...">Discover our Global Benefits</a>

That’s not what we expect for the default English locale.

5. Client (via DevTools Elements tab) eventually shows:

<a href="/book-a-demo" class="...">Discover our Global Benefits</a>

which is correct.

Expected Behaviour

• The server‐rendered HTML should show href="/book-a-demo" for the default locale, matching localePrefix: "as-needed".

Additional Details / Screenshots

• Our next.config.mjs:

import createNextIntlPlugin from "next-intl/plugin";
import { withSentryConfig } from "@sentry/nextjs";

const withNextIntl = createNextIntlPlugin();

/** @type {import('next').NextConfig} */
const nextConfig = {
  trailingSlash: false,
  // no built-in i18n config
  images: {...},
  rewrites: async () => [...],
  async redirects() {
    // ...
  },
};

export default withSentryConfig(withNextIntl(nextConfig), {...}, {...});

• We do not have a built-in Next.js i18n block in next.config.mjs.
• Screenshot of “View Page Source” with /en/book-a-demo (attached).

• Screenshot of “Elements tab” showing "/book-a-demo" (attached).

Expected behaviour

We believe localePrefix: "as-needed" should prevent "/en/" from appearing at SSR for the default locale. Yet the SSR HTML still includes "/en", while the client re-hydrates to the correct "/". Any guidance on how to ensure the SSR output fully omits "/en/" for English would be very appreciated!

Thank you for your time!