I'm using the German version of the game and the trainer works fine. If you have trouble I suggest you grab the executable from any questionable source and try it again.
I have to admit that I'm using the steam version. There will be a difference between steam and retail version.
Piranha Bytes made a special retail version in Germany which is DRM free (Still uses a disc check though.) thus the exe differs from the "default" steam version of the game.
The trainer is nice but it won't help against bugged quests, missing items or NPCs and gamebreaking glitches. And those are bound to be in here en masse since it's the 1.0 version of a PB game. 😵
Thats one good thing about Gothic/Risen games they are mostly beta tested to death, unfortunately Gothic 3 was an exception, the rest however was tested to find as much bugs as possible.
The Gothic community is always good like that.