[BUG] Incorrect metadata canonical URL with next-intl

[enterwiz]

Describe the bug

When using next-intl in as-needed mode, the canonical URL in metadata shows the correct path (https://mysite.com) during next dev, but incorrectly appends the default locale (/en) during next preview or production builds. This violates the as-needed mode specification where default locales shouldn't appear in URLs.

Steps to reproduce

1. Create a Next.js project with nextjs, opennextjs and next-intl (v3+)
2. Configure i18n with as-needed mode:

   // middleware.ts
   export default createMiddleware({
     locales: ['en', 'zh'],
     defaultLocale: 'en',
     localePrefix: 'as-needed'
   });

3. Set metadata with relative canonical:

// app/[locale]/layout.tsx
const metadata: Metadata = {
  metadataBase: new URL('https://mysite.com'),
  alternates: { canonical: './' }
};

4. Run next dev → Open /en → Canonical shows https://mysite.com (correct)
5. Run opennextjs-cloudflare build && opennextjs-cloudflare preview → Open /en → Canonical shows https://mysite.com/en (incorrect)

Expected behavior

Expected behavior​​

Canonical URL should consistently omit default locale prefixes in as-needed mode across all environments:

• Dev: https://mysite.com
• Preview/Production: https://mysite.com

@opennextjs/cloudflare version

1.0.4

Wrangler version

4.19.1

next info output

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.5.0: Tue Apr 22 19:53:27 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T6041
  Available memory (MB): 24576
  Available CPU cores: 12
Binaries:
  Node: 22.11.0
  npm: 10.9.0
  Yarn: N/A
  pnpm: 10.8.0
Relevant Packages:
  next: 15.3.3 // There is a newer version (15.3.5) available, upgrade recommended! 
  eslint-config-next: 15.3.3
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.8.3
Next.js Config:
  output: N/A
 ⚠ There is a newer version (15.3.5) available, upgrade recommended! 
   Please try the latest canary version (`npm install next@canary`) to confirm the issue still exists before creating a new issue.
   Read more - https://nextjs.org/docs/messages/opening-an-issue

Additional context

No response

[vicb]

It looks like you are using a relatively old version of the adapter.
Chances are that this is already fixed in the latest version.
Please give it a try.

[enterwiz]

It looks like you are using a relatively old version of the adapter. Chances are that this is already fixed in the latest version. Please give it a try.

upgrade @opennextjs/cloudflare to 1.4.0, the problem still exists.

@opennextjs/cloudflare: 1.4.0
@cloudflare/workers-types: 4.20250711.0
wrangler: 4.24.3

[vicb]

Please attach a minimal repro (link to a GH repo) and then you can re-open the issue.
Thanks!

[enterwiz]

Please attach a minimal repro (link to a GH repo) and then you can re-open the issue. Thanks!

Hi! I created a project for test this scenario.

https://github.com/enterwiz/opennext-canonical-test

@opennextjs/cloudflare is upgraded to 1.5.1

When using npm run dev, all the canonical of the paths below are correct. However, using npm run preview, the canonical is wrong when changing to the default en locale (with unexpected /en prefix).

Please check these URLs:

URL Path	Expect Canonical	Actual Canonical	is i18n route	is correct
/	http://localhost:8787/	http://localhost:8787/en	Yes	No
/without-i18n	http://localhost:8787/without-i18n	http://localhost:8787/without-i18n	No	Yes
/with-i18n	http://localhost:8787/with-i18n	http://localhost:8787/en/with-i18n	Yes	No
/de/with-i18n	http://localhost:8787/de/with-i18n	http://localhost:8787/de/with-i18n	Yes	Yes