If you've set a language on your operating system that defaults to right-to-left interface orientation, is there any reason that you'd like to set it to left-to-right anyway? Because you might already be used to it that some applications don't support RTL?
Or asked differently: Does it make sense to add a RTL/LTR setting so that the user can decide? Or should you just force RTL interface orientation when the language is e.g. set to Arabic?