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