I'm not talking about books for learning foreign languages, although there are plenty of those. I'm talking about books written for native speakers. I didn't realize there were so many books in different languages on Amazon. It's not immediately obvious how to find these books on the site and it seems like they hide the foreign section or at least they don't really care if you find it or not. It took me a bit of searching and I eventually stumbled on it by accident. If you go to "Advanced Search" it only lets you choose English, French, German, and Spanish.
Typing "Arabic" into the search is just going to give you books for learning Arabic. If you want authentic books written for native speakers of whatever language you're looking for then you need to go here. That link takes you to where you can view all the foreign language books on Amazon.com sorted by language. As you would expect, there are a ton of books in Spanish, French, and German, but they have less common languages as well. There are nearly 20,000 books in Arabic and 500 books in Farsi. They even have languages like Armenian, Bengali, and Malay.
I bought The Crime in Arabic by Naguib Mahfouz and a book of Arabic short stories that has both Arabic and English. I'm trying to do more reading in MSA. Reading is something that I haven't focused a lot on and so I feel it's a skill I am weak in.
I hope this was helpful. I've been trying to find a place that sold Arabic books that shipped to the US. I didn't think Amazon did it because I could never find anything but books for learning languages. Maybe they don't advertise this because there isn't a big demand for it? But eventually languages learners need to move past books that teach language and on to real authentic materials written in the foreign language.