I have the same, uh, "problem," maybe. I can translate mahjong theory by sight, especially beginners.biz as the author doesn't use a wide range of words and likes repeating them quite a few (「もっとも」「のでしょうか」「比較」等々... whoever gets to say how many times the author said "最も" gets a free coke), and I can read smoothly through it, but when I pick up an actual Japanese book of, say, Science Fiction, I'm completely lost. And it's funny, because the normal Japanese fella can't read mahjong texts correctly if he doesn't know a thing about mahjong, as most terms are chinese in nature (起家(ちーちゃ)?あ?「きか」?)....Without really trying I've also picked up several dozen kanji (in addition to the winds and numbers*) and can recognise most mahjong terms by sight, although that's not much use in everyday life! I've not really learnt any vocabulary or syntax...
So, I want to use this skill at least... given that I can't really use standard Japanese (save for some Kansai-ben but that's a completely different matter).