Catch all route within dynamic segment breaks dynamic params

Link to the code that reproduces this issue

https://codesandbox.io/p/devbox/optimistic-brahmagupta-qcqflx

To Reproduce

1. Start dev server
2. Change locale to be anything but en
3. Page is being rendered / no 404 even though there is dynamicParams = false on the locale's segment level

Current vs. Expected behavior

Following the steps from the previous section, I expected /de to render a 404, as dynamicParams is false and de ist not listed within the segment's static params. Somehow the nested catch all route breaks this behaviour and makes it fall back to a dynamic behaviour, trying to render the given locale, running into errors because the locale does not exist.

Provide environment information

Binaries:
  Node: 20.9.0
  npm: 9.8.1
  Yarn: 1.22.19
  pnpm: 8.10.2
Relevant Packages:
  next: 15.0.0-canary.140 // Latest available version is detected (15.0.0-canary.140).
  eslint-config-next: N/A
  react: 19.0.0-rc-7771d3a7-20240827
  react-dom: 19.0.0-rc-7771d3a7-20240827
  typescript: 5.3.3
Next.js Config:
  output: N/A

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

Navigation

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

next dev (local), next start (local), Vercel (Deployed)

Additional context

No response

Open the linked CodeSandbox and run the reproduction steps with a non-en locale. Trace the dynamic locale segment and its nested catch-all route, then verify that /de returns a 404 when the segment sets dynamicParams = false and de is absent from its static params.