Completed and improved German translation

[msiism]

No description provided.

[raphaelahrens]

I would suggest to change
"Maustastenbelegung mit ungültiger Taste "%s""
to
"Ungültige Maustaste "%s" belegt"
or
""%s" ist eine ungültige Maustaste"

[msiism]

Thanks for having a look!

However, I don't see the need to make any of the changes you suggested. While your translations are shorter, the one I chose is the least ambiguous of all three versions and I think that unambiguousness is more important than brevity here.