Who thinks it is needed a magnifying glass to be able to read Arabic on this course?
Yes, it's very hard to read the font that Duolingo has chosen for arabic, at least on the 11-inch MacbookAir that I use.
Before I gave up on the arabic course, I used the mobile browser and had to zoom in all the time especially when there were diacritics, those are impossible to read otherwise.
I was looking at the arabic fonts on my Mac and found that the one which is easiest to read, to me at least, is called "KufiStandardGK". The font which Duolingo instructs browsers to display is called "GeezaPro", one of the more difficult ones to read.