Ehh...I think he mentioned in the Art of Discworld that their jargon was a bit of Scots and a bit of made up stuff and a few other things, and of course they owe a lot to the Picts, who are the people who USED to live where to Scots are now. Something somebody said earlier in this thread intrigued me... The Nac Mac Feegle were "more believable than Roundworld fairy tales of pixies" and things. They're certainly more fleshed-out, but plenty of the old elves ('elf' used here in the broadest sense of the word) were sort of like them, in various ways.

Good and evil came up, too. I think...the Queen is 'evil' but she doesn't KNOW it; hasn't the capacity to know it, I think...remember Lily Weatherwax? It's a type of evil he seems to like applying to females. Hm, there's a thought. First one I've produced today! Wow, I'm going to bed....