Would 日本語をわかりません。also work?
が is the particle used with わかる
It should (as long as you use が instead of を).
Will check back on this later.
That was my answer and it accepted it
を should be just as good. I can't tell you the specifics of why though.
It's a little silly to require the 「わたしは」 here, I feel. The topic is pretty well implied.
I just helps to imply that you can't speak Japanese well ;)
Why isn't this わかっていません?
That translates as "I am not understanding" so has a slightly different meaning.
Why "ga"? Isn't it a subject particle? "Japanese" is not the subject here, the person is!