I have this problem as well.

I previewed the citation in the Zotero Preview Pane (chrome://zotero/content/tools/cslpreview.xul), and it looks like the translator's name appears fine in some of the Chicago styles, but not in MLA or in Chicago (Author-Date) or Chicago (Note without Bibliography).
Can someone fix this, please? It's pretty important to credit the translator. Thanks.

Sorry, should have mentioned that I can't get the Translator to appear for a Journal Article item type. The Translator field comes up fine in the Book item type.

An example -- I get this:
Derrida, Jacques. “Telepathy.” _Oxford Literary Review_ 10 (1988): 3-41.

...instead of this (which is what I want):
Derrida, Jacques. “Telepathy.” Trans. Nicholas Royle. _Oxford Literary Review_ 10 (1988): 3-41.

Thanks for the fix. There's one more tweak needed with the translation field in MLA -- the Translator credit appears in the wrong place for a Book Section item.

What I want is this:
Lyotard, Jean-Francois. “Acinema.” Trans. Paisley Livingston. _Narrative, Apparatus, Ideology_. Ed. Philip Rosen. New York: Columbia University Press, 1986.

What I get is this:
Lyotard, Jean-Francois. “Acinema.” _Narrative, Apparatus, Ideology_. Ed. Philip Rosen. Trans. Paisley Livingston. New York: Columbia University Press, 1986. [translator appears following the book title, rather than following the section title]

Seems minor, I know, but this error makes it seem like the whole book is translated by Paisley Livingston, whereas it is only the section/chapter that is a translation.