Basically the entire Japanese OSS community runs on Twitter. It's their medium of choice for communication, which is great since discussions are very very open (it's facilitated by their language's much higher information density compared to English, probably ~5x).
The vast majority of the contributors are eager to talk to users around the world, so if you use a project with a known Japanese maintainer, try shooting them a message on Twitter. Their English may be broken at times but you can usually understand what they're saying pretty easily.
The vast majority of the contributors are eager to talk to users around the world, so if you use a project with a known Japanese maintainer, try shooting them a message on Twitter. Their English may be broken at times but you can usually understand what they're saying pretty easily.