The Supernal language is the language used by the gods, shared with angelic servants and also known by devils. It is written in a system of hieroglyphics. It is a universal language, where listeners who don't speak supernal will understand the words as if the speaker used their own languages. The gods and angels may choose to disguise their speech if this is not desired. Additionally, supernal contains words of power, which include the raw magic of creation. [DMG:171]
Each race heard the supernal language in a different way, resulting in the various languages among the different races.
This language cannot be selected as a 1st-level character, but could be learned through the linguist feat. Should a mortal learn the language, they don't gain the ability to be universally understood, nor can they exploit the words of power.
Note that some GMs may have a house rule preventing players from learning supernal.