Japanese psychedelic band Kikagaku Moyo writes lyrics that are basically Japanese baby talk / babble.

https://youtube.com/watch?v=idfOZFdTM-8&t=2m39s

https://genius.com/Kikagaku-moyo-dripping-sun-lyrics

And let’s not forget “Ken Lee”

https://youtu.be/vUAaHkGpJy8

Or Dead Can Dance, e.g. https://www.youtube.com/watch?v=VEVPYVpzMRA .

It's harder to generate good gibberish than it appears at first.