My best advice would be: don't touch it. The user knows better what keyboard layout to use and when. Besides, you will badly hurt the user who want to use their own layouts for some language.
My second advice would be: at least, don't even think about switching of the system-wide switch. If you really need to switch the keyboard by your code, switch the input language instead, only for your application. This is how:
But I still think that not doing anything is much better. Remember, Arabic language is very popular; and the Arabo-Persian script is even more popular, so it is supported by default by nearly all modern systems. No need to add anything else to it. Even I, barely understanding just 2-3 Arabic words, personally used to write the text in this script for software testing purposes. For me, it was quite difficult, but for your customers… :-)