Japanese carrier Softbank Mobile will also be updating its HTC Desire to Froyo, via an over the air update starting Oct 8. It appears it will have the same system (with Japanese language support of course) as all its North American and European counterparts, including full support for Adobe Flash. A much better translation of the official blurb than the Google Translate version:
Softbank Mobile has announced that they will commence an over the air update for their HTC Desire customers on 10/8. The update will upgrade the phones to Android 2.2, with Flash 10.1, 720p camera, SD card storage for applications, and some native language sorting problems will be solved.
[Softbank (Japanese)] Special thanks to Christopher for tip and the translation. Domo arigato!