Okay, so I learned a little while ago that
私は日本語を悪いです
is what you should say.
But someone who is Japanese told me that
私の日本語わ悪いです
is correct.
So now I'm a little confused. Are both correct? What are the differences; do you use the sentences in different situations or something?
I think you probably meant to write:
私は日本語が悪いです。(Lit. As for me, Japanese is bad.)
私の日本語は悪いです。(Lit. My Japanese is bad.)
The word 悪い is a literal translation of the English 'bad'. In Japanese, you don't use 悪い to say you're not good at something. Instead, I recommend saying:
私は日本語が[下手]{へた}です。(Lit. As for me, Japanese is poor/unskillful.)
私は日本語が[上手]{じょうず}ではありません。(Lit. As for me, Japanese is not good/skillful.)
私の日本語は[下手]{へた}です。(Lit. My Japanese is poor/unskillful.)
Grammatically speaking, both 「私は～が・・・」 and 「私の～は・・・」 are acceptable here (though the focus might be different). Similarly, you could say:
山田さんは[髪]{かみ}が[長]{なが}いです。(Lit. As for Yamada-san, hair is long.)
山田さんの髪は長いです。(Lit. Yamada-san's hair is long.)
to say 'Yamada-san has long hair'.
The first one is absolutely not what you should say; it doesn't make any sense since you're pairing the direct object particle を with an adjective.
The correct way to say what I think you're trying to say would be "私は日本語が悪いです." The second one also works, although the orthography is wrong; わ should always be written は when used as a particle.
