I was going to mention scat, but there is no secret language involved (in the sense of having grammar and systematic idea-utterance mappings), only use of syllables to create an articulated sound or to imitate other instruments.

Looking at my notes, I find that the consonant-less singing was part of a practice called "jubilus singing", a form of ecstatic singing in the Christian patristic period, where singers would improvise using words from sacred texts. "It is a certain sound of joy without words...it is the expression of a mind poured forth in joy..." (St. Augustine) I first learned about this from a recording of David Hykes, who combined it with overtone singing. There are quite a few samples of Hykes and his Harmonic Choir on YouTube. For instance, Brotherhood.