I do too (and think all people should), but that rarely goes much beyond "yes", "no", "hello", "goodbye", "please", "thank you", "sorry / excuse me" and the numbers from one to ten. And that's not enough to understand an explanation on an aikido technique.
The Japanese required to understand an explanation of an aikido technique is exceedingly easy, especially since many of the key words are in the techniques themselves. If one is going to Japan to study aikido there, I think it would behoove them to learn the basic body parts: te, ude, hiji, ashi, tsumasaki, koshi, kata, mune. As well as directions: ue, shita, migi, hidari. If one was feeling really industrious, one could learn some basic verbs of movement: hairu, sagaru, kimeru, hineru, nageru, ageru. With this basic lexicon, combined with a little broken English that almost any Japanese person can do, one could get a lot out of an all Japanese class.
Previous to a trip to Zurich, I bought some teach-yourself German books and went through them in the months before my trip, paying special attention to German I was likely to use: shopping and getting directions. Of course, this did backfire, as when I bought a box of Swiss chocolate. I said, "Ich möchte diese Schokolade kaufen" in what must have been rather passable German, as the Verkäuferin responded in a string of rapid-fire German that left me weeping on my knees.