Text shows in wrong language

The first language of our homepage is German. Since a while, it automatically translates some bits of the event calendar (we use the “events calendar PRO” plugin) to English, when being on the German version of the page. If you use the link above you will see that instead of “Januar”, it is written “January”.

I checked already the loco translate plugin for the events calendar pro. The translations there are all correct and complete. Would you be so kind and help me figure out where the problem lies?

Thanks + kind regards

The page I need help with: [log in to see the link]