Grüezi Monika,
Thanks for using our plugins and for reaching out! I’m sorry you are having this issue.
This seems to be a small glitch, which I will forward to the developers for a fix.
Meanwhile what you can try to do is change the translation from ‘alle’ to ‘all’.
For this you will need to edit the wp-content\plugins\events-calendar-pro\lang\tribe-events-calendar-pro-de_DE.po file. You can do that with the free PoEditor software for example.
Once you open the file look for the string ‘all’ in the source text. The translation should be ‘alle’ as expected.
Change ‘alle’ to ‘all’ and save the file.
Upload the tribe-events-calendar-pro-de_DE.po and tribe-events-calendar-pro-de_DE.mo files to your server to the respective folder, overwriting the old files.
Check your site if this solves the issue.
Let me know how that works out.
Cheers,
Andras