During the Windows Vista event in New York I noticed the new updates including some language packs:
Update: Windows Update just dropped over 20 updates to my Ultimate machine. 7 of those updates are for known issues (HD Audio, FireWire hard drives, and Phishing Filter, among others), 11 are language packs, and 2 are the final versions of the BitLocker and Hold 'Em Ultimate Extras.
Update 2: Do change the language you have to go to Control Panel -> Change display language:
Now, I have Japanese, German and English. ;)