Probably platt deutsch and not hoch deutsch.

I was in a store in Amish country once (this is the first time since 1971 that I have NOT worked in Amish country) with my wife and a friend. The friend was quite fluent in German, and she later regaled us with what the Amish "girls" (not yet churched) were saying. She was especially tickled when one of them made a comment about her and she answered in German -- the young lady was embarassed! (Never use a language that is not your own for making comments about others!)

(The same sort of thing happened to the father of friend in Sneem, Ireland -- the man's home town. He was sitting in the pub, quietly having a pint or six, and he overheard a couple of locals talking about "the yank over there" in Gaelic. Well...I leave the rest of story to your imagination. Suffice to say that the man is very fluent in Irish....)