A huge shout out to Heather Pagan, who helped us with medieval French and edits the Anglo Norman Dictionary. Here’s the official translation of the Medieval French, along with some fascinating notes on historical swearing, which you all know is our favorite!
Go copulate with a pig - Va foutre un porcel! (literally, go fuck a pig). Unless the joke is that they are being formal (ie. copulate and not fuck) in which case: Va couvrir un porcel!
You defend that rampart female? - Femme / Dame, defendis tu le terrail?
To the death, prick*! - Jusqu'a / A la mort, ribaud! OR Jusqu'a / A la mort, paillard! OR Jusqu'a /A la mort, pautener!
* There are lots of words for penis/prick in Old French, but I don't have any evidence that they were used as insults (and that's a whole 'nother book about when we began to use genitalia as offensive words...) I've chosen to translate it with a bunch of words that mean 'jerk'. The words I used are all ones that end up being borrowed into English (ribald, pailliard, pautener) for someone who is base / rascally / a scoundrel / someone of low status etc.
Thoughts (or why you never ask an academic for a translation...) We actually don't know overly much about medieval swearing. What we know about language use during the period is based on what was written down, and what was written down (gross generalization ahead) tended not to be 1) direct / indirect speech or 2) of a less formal register. Nevertheless, we do have some record of what people said, and in some cases, how they would curse each other. A lot of these curses were be religious in nature - damning them, accusing them of bad faith etc. We have one amazing set of texts, referred to as the Manieres de Language, which were an early type of phrase book for Englishmen wanting to learn French in the late fourteen century. These include my favourite section - insults! So this is mainly what the translation is based on - though insults of the time were a bit different.
Here are some from the phrase book (translated): You're lying, you evil bastard; Go hang yourself, you bastard; Go away you bloody son of a whore; You will pay!; Kiss my ass (I am very pleased that this has been the eternal insult!); Kiss the devil's ass; Go to the devil!