In previous version of adobe Illustrator, I was unable to write Arabic there. I had to do is enable Arabic to purchase a Middle East version or use InPage, alternatively. But Adobe Illustrator CC makes me happy to remove my defects, Finally. You just need to follow a simple task to achieve it.
Go Edit > Preferences > Type > Show Indic Options : Check it. > OK
Restart Illustrator and Enjoy !
Now see : How to Enable Arabic Writing in Adobe Illustrator CC