There are simply far more Germans than Bohemians, and the language of trade and communication through the Empire is going to still be primarily German based on those raw demographics, which is going to increase the prestige and usefulness of German language, and by extension the attractiveness of German culture. At best, if you're very successful in placing Bohemian tutors and advisors with all the princes of the little German states, (which is a big if, given how these advisors would likely be seen as obvious agents of a dissimilar Emperor) you might wind up with a lightly Slavicized elite ruling over a still thoroughly German population, who will quickly re-Germanize the moment the Bohemian dynasty weakens its grip. As stated previously, the more likely option is that the weight of the German cultural sphere is going to slowly Germanize Bohemia. Consider the examples of places like China or Iran, which have assimilated various waves of invaders and foreign dynasties over the years based on similar demographic factors.