Uh oh! If you’ve been pre-loading Diablo 3 in English or German, you may have to take another look. According to a post on Battle.net this afternoon the current downloaders may not be working properly in getting you all the files you need. Don’t panic though, you won’t have to re-download the entire game.
Just get the new downloaders from Battle.net and point them at the file where you installed the game previously. The new installer will download a 65 MB patch that should fix things. You -must- get the new downloader though, even if you want to do a full reinstall. The old program will not be able to run the game come launch.