If a translator’s name is not provided in the source, then skip that element in your works-cited-list entry. Follow the MLA template of core elements, leaving the translator’s name out of the Contributor element:

Baudelaire, Charles. “Autumn.” My Poetic Side, mypoeticside.com/show-classic-poem-2171.

Crediting authors and contributors is essential, so if you know the work you are citing has been translated, always be sure to check the source thoroughly to see if a translator’s name is included anywhere.