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.