Tom, I am speaking from ignorance here, so this is a genuine question, but what does "Pre-Celtic" actually mean? (I once heard a radio programme in which a historian put the view that the idea of Celts is a modern construct and there was no such group, but that's all I can remember.) What period of time? Do you / the book you cite suggest that the Druids had their own language, or is this just suggesting a period of time? I'd love to know.

Seems to me that even if *some* ancient words appear as apparent nonsense in songs, doesn't mean all the apparent nonsense is made of ancient words. I thought much of it was mouth music, rhythm with no intended meaning.