The following etymology is suitable to a book of Phrase and Fable. It is said that one Latan, a famous quack, used to go about Paris in a gorgeous car, in which he had a traveling dispensary. A man with a horn announced the approach of this magnate, and the delighted sightseers used to cry out, “Voila! le char de Latan. ” When I lived in Paris I often saw this gorgeous car; the horn-man had a drum also, and M. Latan, dressed in a long showy robe, wore sometimes a hat with feathers, sometimes a brass helmet, and sometimes a showy cap. He was a tooth-extracter as well as dispenser.
Probably “Latan” was an assumed name, for charlatan is undoubtedly the Italian ciarlatano, a babbler or quack.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894