grammelot
A style of language used in satirical theater: a gibberish with macaronic and onomatopoeic elements, used in association with mime and mimicry.
countable, uncountable
Actually, much of “Mistero Buffo” doesn't require translation and indeed is untranslatable: Mr. Fo speaks in “grammelot,” a kind of polyglot gabble speckled with an occasional intelligible word.
Where it comes from
Unknown. Dario Fo claims a French origin, and it has been linked to grommeler (“to grumble”).
Adapted from the Wiktionary entry grammelot (CC BY-SA 4.0).