Learn latin, spanish, chinese etc that are more wide spread. I love Japan and want to return after spending a week there but I wouldn't learn a language I'm not going to use long term. Maybe trial a few lessons and see how you feel about it. The main thing about the other languages I mention is if you speak chinese you can often understand many other dialects, japanese included. If you speak latin you can understand spanish or italian etc. So maybe learn something more usual if you're going to invest in a second language.