"She speaks Chinese badly."
Translation:Ŝi malbone parolas la ĉinan.
Don't bet your life on what I say, but since the adverb is preferably put before what it modifies, this sentence would seem perfectly correct to me, only meaning "Chinese she speaks badly (possibly something else very well)".
For the given general sentence, the adverb should be before the verb, or at the end of the sentence.
How would one differentiate between Mandarin, Cantonese and Hakka?