Celestial

One of the Six Eternal Languages, Celestial is the tongue of the upper planes, spoken by angels, archons, and other denizens of the goodly astral realms. It has two forms: one that can be partially learned by mortals and non-Celestials, a language of such elegance that it makes Aeonesti  sound grating; and one reserved for the Celestials themselves, which can be intoned to cause mortals to tremble in awe, their senses completely overwhelmed. 
Similarly, the writing of Celestial is beyond mortal comprehension--many scholars believe that writing is unnecessary to the higher beings, and any examples appear as excruciatingly blinding light. However, when written in the mortal form, those transcribing Celestial employ the Aeoketh Script, the closest approximation though certainly lacking in many regards.