Next.js returns HTML instead of JSON for _next/data requests

Link to the code that reproduces this issue

https://github.com/arichard-info/next-rewrite-middleware

To Reproduce

1. Clone the repo
2. npm run build
3. npm run start
4. Open the network tab and rollover the link
5. Open the _next/data request in a new tab (for example http://localhost:3000/_next/data/Wyr4K4y9f6V6FjKlwRrH5ee/fr/nice-public-path.json) => you get the page JSON
6. Change the buildId in the request (for example http://localhost:3000/_next/data/test/fr/nice-public-path.json => you get the page HTML

Conditions to reproduce :

• Having rewrite rules in the middleware
• Having i18n configuration in next.config.js

Current vs. Expected behavior

When using middleware rewrites + i18n, mismatches of buildId are not well catched for _next/data requests.

On client-side navigation, the _next/data requests with invalid buildId returns the page HTML instead of a 404. The expected behavior is to get a 404. The _next/data requests should never return HTML content

This causes issues for example when you have a custom cache configuration :
When you are behind a CDN cache and navigate between two pages, if _next/data calls contains the previous buildId, you're getting a broken page

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System:
  Platform: darwin
  Arch: x64
  Version: Darwin Kernel Version 22.3.0: Mon Jan 30 20:42:11 PST 2023; root:xnu-8792.81.3~2/RELEASE_X86_64
Binaries:
  Node: 18.19.0
  npm: 10.2.3
  Yarn: 1.22.19
  pnpm: 8.6.9
Relevant Packages:
  next: 14.0.4
  eslint-config-next: 14.0.4
  react: 18.2.0
  react-dom: 18.2.0
  typescript: 5.3.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Middleware / Edge (API routes, runtime), Routing (next/router, next/navigation, next/link)

Additional context

No response

Clone the linked reproduction, then run npm run build and npm run start with its middleware rewrites and i18n configuration. Start by tracing the _next/data request handling for an invalid buildId; done means client-side requests with a mismatched buildId return a 404 rather than page HTML.