This isn't a language of the gods or celestial beings, it's The First Language , used by those primordial beings before there was sound and light. I mean, technically, anyone can understand it, but not anyone can use it. It bypasses translations and words. Like how some languages are based on intonation or pitch, The First Language is based on conviction and sheer force of will. Lacunas , or words without translation between languages are all over the place because of a lack of context in different cultures. For The First Language however, there are no questions, no expressions of doubt or fear. It's not a matter of being able to intonate or enunciate . Speaking it is a matter of knowing your truth and projecting that forward onto another. Hearing it, if you can even call it that, is knowing and accepting the Truth laid bare before you. If you know it to be true, you understand it. If not, then you don't. If a creature hears it, they make a Wisdom saving throw or ...
Steal everything you see here.