In what movie is this sign posted: “Welcome to Man-drake Falls/Where the Scenery Enthralls/Where No Hardship E’er Befalls/Welcome to Mandrake Falls.”?

Douglas Fairbanks was referring to Adolf Hitler and Charlie Chaplin, who was getting ready to film The Great Dictator (1940), when he said, “This is one of the most fortuitous tricks in the history of civilization, that the greatest living villain in the world and the greatest comedian should look alike”?.