Cypriot Maronite Arabic/Sanna
(This language is not on the list and I have already contacted Lrtward about adding it.)
As you know there are many requests for Arabic. And Duolingo is looking at adding Modern Standard Arabic. Eventually.
I would like to suggest Cypriot Maronite Arabic, also known as Sanna. This language is now listed as severely endangered by UNESCO. Recently there has been some interest in saving it.
One of the advantages of this form of Arabic is that, although it has historically used Arabic Script, it currently uses Greek and Latin scripts.
According to Omniglot "Cypriot Arabic is a variety of Mesopotamian Arabic spoken in the Maronite community in Cyprus. Speakers used to live in Kormakitis (Κορμακίτης / Kurmajit / Kormacit) in northern Cyprus, but after Turkish invasion in 1974 most of them moved to southern Cyprus. There are 3,656 speakers, according to the 2011 census, all are over 30, and none speak Cypriot Arabic as their first language. The language is also known as Cypriot Maronite Arabic."
This sounds interesting to learn. I am melkite, which is somewhat similar to maronite.
I am Cypriot and very interested in keeping this language Alive. It seems to exist in a very secluded village on the coast of Cyprus. Only around 200 people in this village exist. This would be a great addition to Duolingo