I'm working on Malbrouk - the Jersey French version at the moment, and came upon this which suggests the song is far older. (Source here)
Malbrouk or Marlbrough (Marlbro'), does not date from the battle of Malplaq'uet (1709), but from the time of the Crusades, 600 years before. According to a tradition discovered by M. de Châteaubriand, the air came from the Arabs, and the tale is a legend of Mambron, a crusader. It was brought into fashion during the Revolution by Mme. Poitrine, who used to sing it to her royal foster-child, the son of Louis XVI. M. Ar'ago tells us that when M. Monge, at Cairo, sang this air to an Egyptian audience, they all knew it, and joined in it. Certainly the song has nothing to do with the Duke of Marlborough, as it is all about feudal castles and Eastern wars. We are told also that the band of Captain Cook, in 1770, was playing the air one day on the east coast of Australia, when the natives evidently recognised it, and seemed enchanted. (Moniteur de l'Armee.) 1
"Malbrouk s'en va-t-en guerre,
Mironton, mironton, mirontaine;
Malbrouk s'en va-t-en guerre.
Nul sait quand reviendra.
Il reviendra z'a pâques—
Mironton, mironton, mirontaine …
Ou à la Trinité."
The name Malbrouk occurs in the Chansons de Gestes, and also in the Basque Pastorales.
The Jersey version was collected by Kennedy, but he doesn't mention any of the above.