My mistake. My recollection is that CJK support was added to FOSI/TeX early on (first editing, then composition), followed by Arabic and Hebrew.
According to current documentation, Arabic, Hebrew, and Thai are supported in the Edit window, which of course is formatted by FOSI/TeX. I was under the impression that support for formatted output had been added, as with CJK. I wonder why not.
My apologies for the confusion!
Suzanne