This is interesting to say the least. The Japanese version of the Windows Phone SDK 7.1 RC is now available to download for developers based in the country of the upcoming IS12T handset from Fujitsu, which is to launch in the next couple of days. Reported reasoning for the addition of a second language is the high priority for Japanese developers to get apps built for the platform.
We covered the release of version 7.1 of the SDK yesterday, as well as the opening of "Mango" app submissions. All systems are green and our Daniel Rubino rightfully put it: 'go, go, go!'. You can download the Japanese version of the SDK from the Microsoft Download Center.