What's difficult about Japanese -- I've found that this keeps on changing for me as the studies advance. I study Japanese purely for translating purposes and do provisional (poor quality) translations as a hobby.

Currently the hardest things for me are definitely the untranslatable, culture-dependant expressions, plus Japanese idioms that never seem to appear on any dictionary, and finally how to translate keigo. Sometimes these things are just way over impossible to convey in any reasonable way into English or any other target language. Even if there's a roughly "equivalent phrase" available, it's still not the same thing. It feels like the more I learn, the more inaccurate my translating becomes.

Up until recently, kanji was what gave me easily the most troubles. I noticed that the usual way of hammering meanings and writings into my head from the most common to the least common just doesn't agree with me in the least, and was deemed an unavoidable migraine-incentive - until I found the free downloadable first part of this neat little book: Remembering the Kanji I (http://www.nanzan-u.ac.jp/SHUBUNKEN/...he_Kanji_1.htm)

I think the link was from somewhere on these forums. I read it for one evening and the next day counted bit under 100 previously unknown kanji I could still reproduce and remember the meaning for. Truly a personal revolution in kanji studies.