The term "Double Dutch" in the phrase "...speak Double Dutch to a real Double Duchess" is a reference to a kids' language-game, in which kids add the syllable "op" after each syllable of the word. Thus, "hello" becomes "hopellop." The result sounds Gibberish to bystanders but is understood by the kids using it, as a sort of "secret language."
The term "Double Dutch" in the phrase "...speak Double Dutch to a real Double Duchess" is a reference to a kids' language-game, in which kids add the syllable "op" after each syllable of the word. Thus, "hello" becomes "hopellop." The result sounds Gibberish to bystanders but is understood by the kids using it, as a sort of "secret language."