I'm not sure I agree with your second footnote. Beowulf is written in Old English, which is quite hard for modern English speakers to read on account of being German. Middle English, however, I think you'd find fairly palatable. For example, the Peterborough Chronicle (https://adoneilson.com/eme/texts/peterborough_40.html) is _roughly_ contemporaneous with the Tale of Genji and is readable by modern English speakers.
This looked as incomprehensible to me (a native English speaker) as a foreign language, albeit one with a bunch of scattered words I recognized…until I figured out that þ meant th and all the sudden I could mostly read it fine.
The letter “thorn” is still alive and well in Icelandic.
It's also (AIUI) pretty funny, in that it's the reason many people seem to think that the word “the” used to be pronounced as “ye”: The letter fell out of fashion at around the same time as printing became popular. So many printers didn't have types – you know, the little mirror-image single-letter lead stamps you compose the page you want to print out of; typesetting – for it. But since the capital “Thorn” apparently looks a bit like the capital Y, they used that in stead. That's where all the “Ye Olde Shoppe” come from: People never said “ye”; it was just a kludge attempt to spell “the”.
