The reference to 'Frog and Mouse' above reminded me of the version

(Frog he would a-wooing ride)
learned, I am sure, in 'Singing Together' when Adam was in Babygros :-)

The Frog he would a wooing ride,
Whipsey diddle dee dandy dee (bis)
The Frog he would a wooing ride
With sword and buckler by his side
With a harum scarum diddlum darum
Whipsey diddle dee dandy dee.

Nonsense in other Celtic languages, too - the Welsh song "Migildi Magildi, Now, now, now" ?

Old Jack Braddlum ? 'Hey ! What country folks we be'.

Fal dee roo dee lam tam
Too lee riddle dee
Trillam tam tillam tah-nee
Praising loud the evergreen,
The tree whose name is the Holly.

I can't see what the point is in any of these, only (as someone observed earlier) that they are fun to sing.