Hi Cliff!
As I mentioned in my first post we already downloaded AND installed the most recent versions of the .po and .mo files for the Events Calendar Plugin, the Events Calendar PRO AddOn and for the Events Calendar Community Events AddOn. We did all the steps that are mentioned in those instructions.
Furthermore we’re using the most recent version of WordPress (4.5-de_DE) and set the Language (Settings → General) to German.
Do you have any other idea to solve this issue?
Thanks a lot!!!