We found 3 Reddit comments about Schwetz mol Deitsch. Here are the top ones, ranked by their Reddit score.
I live in that area of PA and I work for a guy who's fluent in it. I also used this book (Recordings which can be found here, at least for the first half), this book, and this dictionary. There are some older grammars and dictionaries I dipped into, as well as quite a few cultural resources, but those are the big three. I can go into some others if you'd like.
I investigated Pennsylvania Dutch back when I was learning German. There is one textbook available for learning the language. Schwetz mol Deitsch!
Here is a free (very, very) basic course for PA German. There's also this book and this one.