books aren’t just what we do, they’re who we are

Ask Daphne! No one understands me!

Traditional Japanese shoes for Tiffany, who writes:

I wrote a Japanese grammar book. I’ve submitted my book to a number of agents who specialize in education but have never received a reply – because they don’t speak Japanese! The agents have no way to judge my book. My searches for literary agents that specialize in foreign language books has proven fruitless. I don’t know what to do.

Unlike the mainstream fiction market, I think you need to be dealing with educational publishing, Tiffany, which works on a vastly different set of rules than commercial publishing. I think a lot of educational houses happily accept unsolicited manuscripts, and you should check that route out.
The other thing to be aware of, though, is what sets your book apart from other Japanese textbooks. Check out a local college bookstore for what foreign language texts are out there, see who’s publishing them, and see if you’re covering the same material that’s already readily available to educators.
Unless you can find a way to make your book more mainstream — in the way, for instance, that Eats, Shoots & Leaves by Lynne Truss did for punctuation — I would stick with the educational market, and wish you luck!