I'm trying to rewrite non-localized paths (e.g /page1) to localized ones (/de/page1) and therefore I'm seeking help to get the following to work:

• "/de" or "/en" should NOT be matched

• "/de/anything" or "/en/anything" should NOT be matched

• "/test" or "/test/anything" should be matched

• "/deno" or "/end" should be matched

With my current implementation which is based on:

I can get the first 3 of 4 requierements, but can't prevent "de" from also matching "deno".
It seems like instead of allowing any chars which are not "/" after the lang segment, I would need a solution which allows either an exact match or a wilcard which must be preceded by another "/". (So both /de and /de/anything would be covered).

Segmenting these values any further is not a requierement as I'm taking req.url as a whole and only prepend the locale.

This sandbox should probably make it easy to get what I mean:
https://codesandbox.io/s/path-to-regexp-demo-c9efk?file=/src/index.js
(Result is in the console)

I got a bit stuck here, and any help is appreciated, thank you! :)