I like Arabic being on Duolingo, but...
It's too bad it doesn't have a Religion skill like in Hebrew and some other languages that have it
The Arabic tree doesn't even teach verbs. The tree needs to be expanded, it's too soon to ask for such skills, while the tree itself doesn't cover the language.
Arabic was only released a few weeks ago and the course is very short. I'm sure it will be expanded in time, and perhaps they will (with great care) add such a skill when it is.