Installed everything new now it shows me:

ASSERTION d\:code\projects\c++\linkermod\components\shared\shared_utility.h(51):
*opcode == 0xE9

What the hell does this mean? Why won't this game start, damn it. 

As a fellow german, with the same error code, here is my explaination or at least my guess as to why this happens:
We have the german "cut" version of the game, this hinders us to play the mod, i get the same error code with the AT uncut patch but i manage to start the game with the US uncut patch, the problem comes after you select the mod you want to play: "console/font not found", this error occurs when you try to play the game in a language that is not supported by your default game, therefore either the mod author finds a way to fix this or we'll be unable to play this mod with the german steam version.

If i'm mistaken i'm sorry, this is just the conclussion i came to after playing around with different gamefiles (US and AT).