R. Pfeiffer writes the following on the origin of such terms as ‘kitchen Latin’ in the context of the dispute between Lorenzo Valla and Poggio Bracciolini over Latin style. Valla wished ‘to fix a strict definition of the ancient ‘usus loquendi’ from Cicero and Quintilian, and to demand that the recognized veritas, the truth, should be valid for the present and for all time.’
Since Poggio would never have dreamed of accommodating his beloved Latin to such demands, their quarrel was hardly avoidable. The most brilliant piece in this exchange of scurrilous invective was a so-called ‘apologus’ of Valla, a dramatic scene in which the great Italian educationalist Guarino recites passages of Poggio’s Latin letters, and his cook and his groom are to judge the Latinity: Poggio is said to have used ‘culinaria vocabula’, to have learnt Latin from a cook; as a cook breaks pots to pieces, so he smashes grammatical Latin. No doubt the terms ‘Latin culinarium’, ‘Latin de cuisine’, ‘Kuechenlatein’ are derived from this amusing humanistic invention, not from lampoons against monastery kitches at the time of the Reformation.
(History of Classical Scholarship, vol. 2, pp. 35-6)