If you want to change the user interface to Arabic, that's not possible without a jailbreak and advanced programming skills. And most current Kindle models can't even be jail-broken.
If the firmware version of your Kindle is 5.6.5 or lower, you could
jailbreak your Voyage and install an
Arabic keyboard layout.
If you're having problems converting Arabic ePubs to Kindle books, make sure to convert ePubs to AZW3 books with Calibre, because the old MOBi format doesn't work.