Size of vocabulary is the main problem in learning any language. I have the same feeling about Japanese, and had it about English while I was still learning it.
I agree that in Japanese this is exacerbated by the Kanji system, where many words have the same (or very similar) sounds but completely different meanings, and the fact that most words at the advanced level are just two or three kanjis attached together and read in the supposedly "Chinese" way (aka the sound reading).
Having Arabic as a native language makes this even more difficult because in Arabic most of the time if words sound similar it's because they have the same root and are thus related in some way.
I agree that in Japanese this is exacerbated by the Kanji system, where many words have the same (or very similar) sounds but completely different meanings, and the fact that most words at the advanced level are just two or three kanjis attached together and read in the supposedly "Chinese" way (aka the sound reading).
Having Arabic as a native language makes this even more difficult because in Arabic most of the time if words sound similar it's because they have the same root and are thus related in some way.