Hello Manuela,
So sorry for the trouble here with translating the word for Organizer!
It sounds like the PO files might be incomplete or missing a translation string in there for German. You can, however, try using a snippet to translate the word. Here’s an example of how to do that, using Venue as the example.
I’ve also had some luck using the Say What? plugin for on-the-fly translations right through the WordPress admin.
Will either of these two suggestions work for you? Please let me know. 🙂
Cheers,
Geoff