I'd love German voice acting, too, but I guess it would make the game a lot more expensive, since demands for voice acting won't stop with German. French, Spanish, Russian, maybe even Chinese would come up soon afterwards. Therefore I remeber having read a statement by Larian, that they will keep voice acting English only, because of the huge amount of spoken lines once the game is finished.
Surely they can do the three languages of Belgium and have a logical end point.