HT3529: iOS: Using MessagesLearn about iOS: Using Messages
You are totally right! The Persian language pack is really needed in the iOS as well as the Persian Keyboard. Furthermore, using the Arabic keyboard is not a good alternative, since the layout is different and the word suggestion system is really disturbing. The best way is giving some feedback to Apple and hope for a change. You can use Apple's feedback form, or find and sign online petitions and requsts, and try to let them know about our need.