"I don't speak well."
Translation:Non bene loquor.
A poet could get away with it, but it would be far from usual.
Basically, "non" wants to come along before the word it is negating. Here, we do not wish to say that we don't speak, which is what "non loquor" would suggest, but that we speak "not well". Hence "non bene loquor" is better, or perhaps "loquor non bene" or "non loquor bene", though those last two are somewhat less likely for the reason that in Latin we prefer to end a clause with a verb or a noun, not a mere adverb.