You probably only need to go back to the Napoleonic Wars (or any other time - or any time - when the English have decided to hold the French up as an example of all that is execrable ...)

Then how you'll explain that expression with 'Latin'? I may also add that we call it "kitchen Latin" or "backyard Latin" - these are strict translations from Polish, but I also saw such English expression: "dog Latin". Well, it can't be SO old