While this is all good clean fun, the dialog is modern English. Obviously JB is setting something up. I take it to mean that the character comes from the UK. I would assume that if any character survived to a modern age, he would speak a modern language. And if JB decides to introduce some denizen of the UK who has been around long enough to have known at least a couple of wardens from his cell in the well, he will speak in a understandable language.