It looks like Kindle books in Arabic are on their way. "KDP Now Supports Arabic eBooks (Beta)" according to
a post on The Digital Reader.
I did some research and found that a bunch of free Arabic language books were made available on amazon.com about a week ago. There is even a (non-free)
Harry Potter book available.
It appears that Arabic is only supported on the iOS and Android (including Fire OS) apps currently. They cannot be delivered to Kindle for PC or e-ink Kindles.
They also appear to be KFX only. All have Enhanced Typesetting and do not support "Download & Transfer via USB".