I'm German, but when I was playing with the German language file, I've recocgnized, that some words are staying English, as example also with German language there was "Suspension" instead of "Aufhängung".
With this "mod" I've fixed it, as good as my English is. Might not be perfect, but should be a lot of easier for all German users here.
To install just copy the de.ini to assettocorsa -> system -> locales
Assetto Corsa German language file 1.0
German lng file