HI,
despite info gained from various people about the ATC communication in Japan, I learned that they DO NOT speak Japanese on the radio (both mil and civil). During the last 2 weeks I spend at the Japanese airbase and army bases, I only heared the English language. 1 exception was a helo from Kawasaki who speak Japanese while landing at Gifu. But also he spoke the main thing in English (altitude, landing clearance).
So if you go to Japan, just bring your scanner with you. It is generally accepted in Japan and almost every local carries 1 with him or her. Please note that it is also very funny to listen. Calls like: lead back is collect can also sound like evac.
Rgds,
Marco
P.s. if you want more info, please send me a PM as I do not check this forum that often. It can take a while as I am still in Japan doing civil this week.