Wonderful! But I don't think anyone's tried that one yet ....
Hypnosis, though, works by means of suggestion - the hypnotised person is put into a state of deep relaxation and then suggestions are made to the subconcious - you can give up smoking, you can remember XXX or whatever.
One method which does use suggestion is suggestopaedia - but not at the level of hypnosis. And the suggestions don't aim to teach the language as such, but to put the students into a relaxed (but not hypnotised) and motivated state where they are likely to learn more. Those, in my experience work. It also uses various techniques which are intended to direct the language straight to the subconscious for acquisition. I'm more dubious about those. But if you go into the "Teaching ESL" forum, we were talking about it a week or so back and there are some references you can follow up.
I could see someone's language learning benefiting from hypnosis if say they were a learner who'd had a lot of negative experiences with language learning, was terrified of it and sure they'd fail - but for some reason had to succeed. Hypnotism could help them overcome the affective blocks and therefore learn more successfully.