One of my American friends pointed out that the only time she has ever been served 5 different types of potato at a single meal was in Ireland, so there may indeed be something to the notion that we're fond of our spuds. (There were roast potatoes, mashed potatoes, potatoes "au gratin", potato croquets, and some sort of chip/crisp as a garnish, if I recall correctly. Once it was pointed out to me, I noticed it on other occasions, particularly if there was a decent buffet).
English also has "thee", "thou", "thy" and "thine" in church liturgy, but I know of no context where they would be used in everyday speech. Also I don't know whether they embodied a formal/informal meaning when they were part of the living language. I think they were simply second person singular forms.