You'll need at least a 2nd Generation Kindle Paperwhite (the 2013 model) with the latest firmware (>=5.9.6) or the latest Kindle for iOS/Android app. (The Kindle for PC/macOS apps don't support Amazon Arabic Kindle books.)Amazon wrote:Starting today, readers will find a large digital selection of popular Arabic language titles in the Kindle Store including books from leading authors like Naguib Mahfouz, and Nizar Qabani, best-sellers like Al Aswad Yaliko Biki and Harbo Alkalbi Athania (winner of the 2018 International Prize for Arabic Fiction), classics like Ibn Khaldoun’s Muqadimah, Al-Mutanabbi’s anthology, and Kalila wa Dimna as well as translated English language bestsellers like How to Win Friends and Influence People, Diary of a Wimpy Kid, A Tale of Two Cities and Harry Potter and the Philosopher’s Stone. Customers can shop for Arabic language Kindle books on existing Amazon websites including http://www.amazon.com/KindleArabic, http://www.amazon.co.uk/KindleArabic, and http://www.amazon.de/arabischeEbooks.
If you happen to have Arabic epub books, you'll need to convert them with Calibre and the Calibre KFX Output plugin to KFX files. (You'll also need to install Kindle Previewer.)