I'm working on my undergraduate thesis in German Studies (I'm in the US), and the paper is written in German using MLA. There's a quote that I would like to use that was originally in German, but I am only able to get a hold of an English translation of it, meaning that it will have gone from German to English to German. I'll be citing the English source in my works cited, but am unsure of how it should appear in the text. As I understand it, if one is translating from one language to another (outside of a proper, full, stand alone translation of a text), it should be rendered as a paraphrase instead of a quote, but I am unsure of what to do on account of the added layer.
Whether it's a translation or the original, if you are quoting someone else, you should quote them exactly, put the text in quotes, and give a proper footnote. Using someone else's exact words without enclosing them in quotes and giving a citation opens you up to charges of plagiarism.
If you are translating someone else's words -- if your source is in English (regardless of the original language of the material) and you are translating to German, then give your translation and give a footnote saying that this is your translation of, and give the original source.
The part about finding an English translation of an originally German text which you are now translating back to German is problematic, of course. The probability that your translation is exactly the same as the original is very low. But if you can't find the original, that's just how it is. Scholars struggle with problems like this all the time.