RTL stands for Right to Left and is used as the antonym of LTR, Left to Right, in the context of which direction a script runs on a page or other medium.

Many ancient languages were written in various or mixed directions. Today only a few commonly used languages are written in RTL scripts the most significant of which are those using the Hebrew and Arabic families of scripts including:

Language ISO-639-1 code
Hebrew he
Yiddish yi
Arabic at
Persian (Farsi) fa
Urdu ur
Hindi hi
Malay ms
Bosnian bs
Kurdish ku
Uyghur ug

Although historically often written from bottom to top and right to left, 'far eastern' scripts such as Chinese are today as often and quite acceptably written top to bottom and left to right (LTR) in the 'western' manner.

Tiki manages RTL scripts by ... How to manage RTL scripts