Mahyar
Sorry, but I cannot see big differences between two images in your reply. I see that many characters have different form (shape), but the font itself is rendered - drawn - well for me, in both images. Probably the difference in character form is what you're calling "ugly".
I made another example with Vazir font (not Vasir, it's my error). This example is made in Solus Gnome, with Geany text editor.
Vazir Regular 22 pt is set as default system-wide font in Gnome. So Geany interface on the picture - i.e., titlebar, menubar, tab title, line numbers, statusbar - uses Vazir.
The whole text inside Geany is typed in using Vazir Regular 22 pt as well. I added to Gnome two keyboard layouts - Arabic and Persian. Keyboard layout is the only thing which changes inside Geany. It goes from English (US) to Arabic, then to Persian.
Everything on the picture - Geany interface and the text inside it - uses only Vazir font. Arabic and Persian characters (letters?) have slightly different form (or shape), which is probably looks ugly for you. But the font itself is rendered well, for my taste, in all three languages.
I realize that not being Arabic or Persian carrier I can't figure out your needs completely. Just tried to demonstrate that Vazir looks technically well in Plasma and Gnome in all three languages at the same time. There's nothing ugly in them.
Edit: Typo.
