@prof290546: ok, you are new (but personally for me, when I’m new somewhere, I usually spend some time reading “how to use this site”, and at least I would be warned reading the other off-topic “answer” right here, that one starting with “Worked for me too”, with a reply “Please do not use Add Answer if you actually don’t answer a question”).
But anyway, you did not tell what LibreOffice version you were trying to install; what language pack was being installed; what specifically you did (we don’t know if you followed the suggestion to the letter), and what did you see (was the error you finally saw the same or a different).
By the way:
The topic of this post is, that the installation of the German Language Pack is not working
Wrong. The topic was “Can’t install Dutch language pack” (not that it matters though).