hahaha, icelandic has many ways to say hello. Sæll is kind of formal , but friends still use it between each other. You use "sæll" when you are saying hello to male, but "sæl" when saying hi to a female. "Hæ" and "Halló" is wierdly not used that much in Icelandic daily life. Maybe on phone when people can't hear each other or there is a connection issue. Nowadays, especially around the younger generation, it's really popular to greet each other with "sælir" when greeting males, but "sælar" when greeting females. Hope this helps. Good luck learning icelandic!