rtl.css has overridden styles and will load only for rtl languages.
For making a language rtl you must edit "language.xml" file and set "true" for "is_rtl".
Persian language has been translated completely in Crowdin.net and need this changes.
[+] Installer: Add RTL Support with override css file
[+] LO : Added Farsi installer and Installer RTL support
Merge pull request #1 from djfm/rtl
[+] Installer: Add Persian lang and sample data to installer
[*] LO: fix localization for Persian
Great work Danoosh, thank you.