As I point out in What happens during the process of translation?—
[…] a good translation is [one where] you write the text as the author would have if they were a native speaker of the target language. The translated text should emulate the original in terms of the level of literacy, style, and (if someone is being quoted) the socio-economic/educational background of the speaker.
Since not all texts are written well, however, sometimes one must also engage in a bit of farteischt und farbessert (from the Yiddish, “translate and improve”), to convey the writer’s meaning as cogently as possible.
If a translation is meant for publication (or some other form of transmission), anything that clarifies the intended message is welcome.