Here is the "e-reader for Hebrew" thread.
https://www.mobileread.com/forums/sho...d.php?t=105910
It looks like FBReader is hopeless.
Adobe Reader that displays e-pub is the best choice, it seems.
epub file is basically just zip file with html inside. So you can rename it to .epub.zip and unzip it to look inside. Zipping it back, well, that is more complicated, because the file manifest has to be non-compressed inside the archive and has to be at the beginning. Calibre can take the epub apart for you ant then pack it back together. Just right-click on a book in Calibre and select Tweak epub from menu. Calibre will create temporary directory with contents of epub inside. After you play with files Calibre will offer to pack files back into epub.
By the way, OpenOffice/LibreOffice odt files can be renamed to epub and opened on PocketBook, but that is ugly, UGLY hack, because file format is not identical, just similar enough to work (most of the time, in one of PocketBook aplications).