DMRoberts wrote:

Not to mention it's in the AB language, not in Chaucerian London Middle English, which makes it even harder!

I did a little more digging (this book intrigues me for some reason), there is a version translated into modern English by an author Mary Salu, that JRRT wrote a preface for:

https://tolkiengateway.net/wiki/The_Ancrene_Riwle

All editions of it are long out of print, but they're on eBay for what seem like reasonable prices.

There's also a modern English version by author Hugh White that sounds like the translation was based on Tolkien's version.

rosshm16 with good reason!

Mary Salu was supervised by Tolkien from 1941 to 1949, a long process
for a mere B.Litt degree. Incidentally, she also worked for the professor,
compiling indexes and glossaries, a task likely to stall anyone’s progress
even without a war or post-war austerity. Tolkien wrote a two-paragraph
preface for her translation of The Ancrene Riwle (1955). She would later
co-edit the essay collection J. R. R. Tolkien, Scholar and Storyteller: Essays in
Memoriam (1979).

Lepojärvi, Jason, "Companions in Shipwreck: J. R. R. Tolkien's Female Friendships"

I wouldn't be surprised if this translation was the thesis work for her BLitt, but I can't check this.