Also based on this thread
https://www.mobileread.com/forums/showthread.php?t=79709
No reader that is based on Adobe DE (almost all commercial devices with EPUB support) do not handle right-to-left languages properly. That is also my experience.
I just created a sample epub with arabic text embedded font and it is incorrectly rendered in adobe de.
I think the only viable options are:
1. Use only PDF format with embedded arabic fonts for any e-ink device (Sony, Kindle etc.)
2. Get a tablet device that has one of the EPUB readers that do support RTL languages properly. For example iPad with stanza or iBooks or any android or windows based tablet that has Firefox browser where you could install EPUBReader plugin.