I am writing a dissertation for my PhD in Romance Languages. I focus on Spanish literature and use primary sources all in Spanish and secondary sources in Spanish and English, but I am writing in English. Do I need to translate the Spanish quotes I use from my primary and secondary sources into English for my dissertation? I am using MLA style and I could not find a rule about this issue.
I wrote my dissertation about translation in Spanish, and I had to quote several non-Spanish speking authors (English, German, Catalan, French). I decided quoting in the original language and adding the translation in a footnote. When there was a published Spanish translation of the quote, I used it. But if not, I translate it myself. However, it's a good idea to ask your supervisor if there is a style guide for this issues.
The general practice for translation in literary studies is that you translate if your audience does not know the language of the original, e.g. a Russian source on French literature. It may (depending) also be assumed that everybody reads French. But practices change over time, usually in the direction of increasing the need for translation. The best way to determine what the standard practice is in your field is to look at dissertations and academic articles in the field. I note that in some recent issues of Latin American Literary Review, articles in English are published with untranslated quotes in Spanish.