NVDA Japanese team is making the JTalk Japanese TTS as the add-on, which runs on NVDA 2012.2.
It is tested on Windows XP Japanese and English versions.
If you are interested in Japanese speech engine, please evaluate this add-on package.
This package provides JTalk and JTalk2 speech synth drivers.
Note that JTalk2 is experimental multi-lingual engine which uses both eSpeak and JTalk internally.