The venerable Jargon File has the French metasyntactic variables (i.e. the equivalents to foo and bar) as toto, titi, tata and tutu.
Or to take this in another direction: foo sounds like French “fou” which means “mad” (as in “insane”), so “coucou” might be an interesting alternative.










I figure they’re more likely related, in spirit and vocalisation if not etymologically, to the French phrase «et patati, et patata», translatable as “blah blah blah” or “yada yada yada”.