To start using Celestial in game, type -ce console command for Mith's Virtual Console.
Celestial is the common tongue of the Celestial Planes, of Angels, Archons, Eladrin and Guardinals. Any priest or holy warrior who deals regularly with creatures of the Celestial Planes will learn this tongue as a means of communicating with these Celestials. Of course also humanoids with Celestial blood in them know this language. In short, Celestial is a common tongue of good.
On Arelith this language is known by: