The font I use is arial.ttf. I copied it to the directory /mnt/us/fbKindle/qtKindle/lib/fonts, and selected family Arial in the Styles tab in Options dialog. Can you try to use the same font?
I use the same distribution of fbKindle, but I replaced the FBReader binary with one I compiled that fixes some line breaking issues in RTL texts. You can download it from here
. The downloaded file FBReader should replace the file /mnt/us/fbKindle/FBReader .