I have had a request through a Freelang visitor which at first seemed straightforward enough, but which turns out to be beyond my abilities

It involved proof-reading/checking a few English sentences, for which I requested context to eliminate misunderstandings.
The background text is in fact in Latin, which had been translated into French by the requestor (who is French), and which he had then translated into English. But the document dates from the 13th C, and is about 11 pages-long for the three language versions. The requestor would like to ensure the English version flows seemlessly and could not be identified as a translation.
As I have put it to the (charming) gentleman, my problem is that the English language has evolved somewhat since the Middle Ages. I can check his English - which isn't at all bad - but for it to sound authentic, it should be proof-read by a Old English specialist.
I've offered to try and find a volunteer University lecturer, and post a request in this forum. Is there anybody out there who speaks Medieval English?
By the way, the text/challenge is fascinating.
Thanking you in advance,
ChrisP