I went to the US gigabyte site, but they didn't even list that board.
The GA-P55-UD3 is right here:
I suppose it's a leftover file or registry entry that I have to remove... or is the RAID console and service trying to be annoyingly smart and checks sources other than the operating system language? I mean, while the system (Win7) is english, the "location" is set to germany, and the keyboard layout is german as well...
Yes its trying to be smart I think try so try changing the location.
Also you might find that Storage Manager 8.9 is not that stable then 8.8.
You can also install the English-only version of the software package.