Where do you switch the language?

[AnimArts]

I can't find the option to switch this to German. Am I missing something?

[Trendpoker 3D]

Language needs to be switched outside the game by the Steam client:
1) right-click on Skat 3D in your library, then on "Properties"
2) now in general settings you can switch between English and German
3) when (re)starting the game, game runs in selected language

Most Steam games use the same way to switch languages.