So far my only trip to Japan (and probably the only reason I can speak with any proficiency at all) was to the Yamasa institute there in Okazaki. It was a great experience, but if you're not used to speaking Japanese you will have to review a lot of familiar material
until you can speak it. This frustrated a great many students I met, but you've got to trust that the teachers know what they're doing. (Speaking of which,there's sort of a pseudo-mythology on-campus about Yamasa's teachers... how most of them are female, and most of them attractive. No one really knows why. Even so, the favorite of many, including myself, is Mr.
Sugita, a towering 6'3"-something multilingual Japanese man who is an absolute natural at teaching.)
Just stay away from the student village if you like quiet nights, clean kitchens and sane bathroom visits.
If you decide to consider this option and need more info, feel free to PM me or post again here.