On /admin/config/search/path (URL aliases → List) the non-english nodes are linked wrong.

Example
de/node/2839 is the German node, /en/node/2840 its English translation.
The path alias for the German node is Foo ist bar.
In 'ALIAS' column it is linked that way: <a href="/en/node/2839">Foo ist bar</a>
In 'SYSTEM' column it is linked that way: <a href="/en/node/2839">node/2839</a>

So it uses the English path prefix (instead of the German path prefix) for the German node ID.
If you click at that link, it leads you to en/node/2840 (instead of de/node/2839).


All non-english nodes are linked with their NID and the English path prefix in the 'ALIAS' column. Only English nodes are linked with their path alias.

Comments

test one thing, switch the ui language and look at the paths again.

Yep, you're likely browsing the admin UI in English.