Arabic or Hebrew languages.
I think, that should be made an Arabian or a Hebrew language cours, because I think, that these languages is cool, and is a lot of people, who wants to or would like to learn which of these languages. Maybe these languages are difficult, but if you want to learn, you will learn. What are you thinking about?
By "Hebrew languages" I'm assuming you mean modern Hebrew as spoken in Israel, and not biblical Hebrew (which isn't used much outside academic/religious domains).
As a native Hebrew speaker I'm all for it, though I'm not sure there's much demand here on Duolingo.
As for Arabic, I'm pretty sure such a course is currently in incubation.
I'd love it if they added Modern Hebrew, but even biblical Hebrew would be better than nothing.