I'd love German voice acting, too, but I guess it would make the game a lot more expensive.
Beside money logistics are another thing. I don't know if Larian has infrastucture of a major behemoth like EA or Activision necessary to do casting and recording in multiple countries they are not based on.
Just for the record: Do you know who was in charge of BG's Polish localisation ?
A small studio called CDProjekt

Of course.