Originally Posted by Britannicus
I made mistake of trying to use a unicode font to test greek compatibility initially. Just today I tried a standard ancient Greek font (SPionic) and it worked out great (so long as you switch the to the appropriate font for appropriate epubs). I assume the same is true for many other languages.
Check the font I've suggested to the guy that made the test I've linked above... it supports full 65536 unicode characters so it should be ok even for greek.