i had the german steam version too though i could start it with plutonium but in zombie mode when the text for buying a weapon or fixing windows etc appeared it said for example "zombies_kar98_200" then i tried the repair game files thing from the support with the torrent file and everything and it fixed that
also it turned the language to english and the launcher doesn´t go to downloading files for a minute or so after opening but instead opened almost instantly the launcher
so i guess the german steam version might not work all too well