I have been able to read Arabic epubs on Pocketbook PB 600. Once you fiddle with the machine a bit, text looks very good, is indeed formatted right-to-left, with properly combining letters, etc. It does require some fiddling as I detail in the thread below:
https://www.mobileread.com/forums/sho...ariwa55&page=2
I have since upgraded to FW 2.1.2. Re Arabic issues, nothing has changed since what I explained in the thread I just mentioned.
I produce Arabic epubs by converting HTML files from the internet with the grabMyBooks add-on to Firefox. It works very well for the purpose.
PocketBook does have its problems (expensive, buggy software, etc.), so I do not know if I would recommend it. What annoys me is that they seem to pay no attention to bug reports in MobileRead Forums.
I have read through various threads, and I don't see any convincing evidence that any other e-reader handles Arabic any better than PocketBook. But I really don't know. I would like to try Onyx Boox, which does sound promising.
The problem is that the few people interested in reading Arabic epubs seem content to read on their iPads.
Another issue is how to edit Arabic epub files. Sigil displays Arabic fine, but it is nearly impossible to use. I guess this should be a separate thread in the epub section.