AquesTalk TTS 1.1
the author of this app says:
Japanese Text-To-Speech engine.
Read translation, navigation and other apps in a female Japanese voice.
Works great with Google Translation, Google Navigation, etc.
This engine can be accessed via android TextToSpeech API from a variety of applications.
1) Download and run this app.
2) Download Dictionary DIC Settings -> Download Dictionary (>10MB)
3) Go to Android Settings -> Voice Input & Output -> Text-to-Speech settings, activate AquesTalk TTS at the bottom of the screen, then select AquesTalk TTS as the Default Engine.
4) Settings -> Language & keyboard -> Select language, select Japanese.
see also below "Install & Settings"