MHRA: citing texts from foreign language - original in footnotes?
Here a few solutions, all of which should be fine unless your professor explicitly rejects one of them.  Since the MHRA (from what I can tell glancing over it) doesn't include explicit recommendations, as long as you indicate the source of your translated text and the original, I can't imagine them being so unreasonable to count off.


Option 1: Find a translation
This might not be possible, but if you can, just cite it instead.  Life made easy for everyone, unless it's a terrible translation.
Option 2: If short, include both
I would only do this if the handful of foreign words are pertinent to the discussion (perhaps due to ambiguity or double entendre), or are relatively famous.  You would probably want to quote Julius Caesar as …"Veni, vidi, vici" (p. 38), which is to say "I came, I saw, I conquered"….  For such short translations, if you did them yourself or they are well known, there's no real need to indicate the source of the translation.
Option 3: Original/translation in text, translation/original in footnote/endnote.
This prevents your main text from being too cluttered but could quickly turn into an abuse of footnotes/endnotes, especially if you have a lot of relatively short quotes.  If you just have two or three long block quotes, this might be best, though.
Option 4: Translate to English and clarify.
This is my preferred approach.  Just cite in English, but in your citation, add a little extra saying "translation mine" not unlike the common "emphasis mine" to indicate italicization not present in the original.  From what I can tell, in MHRA you actually put "emphasis added" in parentheses inside the quotation marks, so you may just put at the beginning or end "(translated from the French)" or similar.  Or, since MHRA appears to use footnotes for first citations, just include the text after the reference entry "I have translated all citations from this source to English" (or similar), and never worry about it again.