Feels like about a 50:50 split between the English and Japanese speaking players to me, though of course in content that's cross-datacenter we're back to being outnumbered 9:1 due to all the other JP servers in the pool. I don't interact much with the JP players over here so I'll let someone else chime in, but in the meantime you might find this recent document written by one of the local players useful.

https://docs.google.com/document/d/1...F6VYnJm8/edit#