...you're right but why giving the songs German names? Why would Monterey become Sanssouci?
Believe me, Albert... When Germans are capable to dub the entire "Singin' In The Rain" and "My Fair Lady" including the songs, it's also possible in case of "King Of Jazz"... Can you picture Gene Kelly singing and dancing to the song "Singin' In The Rain" in German? YUCK! They did it, really...
Look what I found in the "King Of Jazz" entry on Wikipedia:
King of Jazz was the first motion picture to use a pre-recorded soundtrack made independently of the actual filming. Whiteman insisted that the entire soundtrack should be pre-recorded in order to obtain the best sound, and avoiding the poor recording conditions and extraneous noises found in a movie studio. Universal opposed the idea, but Whiteman insisted and prevailed over the reluctant studio executives. After the sound was recorded, the scene was filmed. Later, the film was synchronized to the soundtrack. This allowed the movie to be directed in the same manner as a silent film, with resulting sounds not affecting the completed film.
This means that it might be possible that the orchestra played the music without the singers and the German singers sang their parts in Germany. I don't know if this was technically possible in 1930...