Isn't that a function of the OS, under linux Tk should check the LANG setting and then handle text based on those rules.
Windows should do the samething if you have the language pack installed and switch to a R to L language.
I only have us-eng installed on my linux box so I can't change languages to test.
It's a function several pieces of software: the font / font renderer and the toolkit the edit widget came from, and sadly the particular application. That's why there are often inconsistencies across systems and softwares. In Windows, the consistency issue at least is better, because one vendor is responsible for more things.
On your linux box where you "only have us-eng installed", you might in fact get BiDi anyway in certain cases (say, for example, in a browser). And to get it *everywhere*, you might have to work very hard.