Regarding what appear to be nonsense words / choruses, there was someone in the North - Shetland? Orkney? Caithness? - a number of years ago who was singing what appeared to be a nonsense song/rhyme- till the right person heard him and realised it was a fragment of Norn, and the song was the remains of the ballad of King Orfeo.

I think there's details of this in John Purser's book (Music of Scotland?) , and I also think I heard Archie Fisher speaking about it on Travelling Folk many years ago -- -

I will take so long to seek out the information I am sure someone will be able to elaborate on this much sooner than I shall!

- However - sometimes the nonsense words are not actually so?!

(I can sing a number of foreign songs eg the Norwegian National Anthem, without having a clue as to what the words mean. I am quick at picking up and remembering songs by ear---some are from over 50 years ago.)