On a recent trip to the Poconos, our family went horseback riding (we found out later that they were really mules). Two of the three guides were actually German and spoke a dialect called Schwäbisch (sounds like shvedish, which is what I originally thought it was; that means "Swedish" in Yiddish), a thick countryside version of German in the family of Alemannic dialects. It has a sing-songy quality to it and is pleasing to the ear. Anyhow, when they heard us singing horse songs (inappropriate to the animal, but effective in spurring them on to go faster) in Yiddish, we got into a discussion about the connection between the two languages. Sabina, the woman (the other guy was her son), explained that there are many words in Schwäbisch which appear in Yiddish but not in standard German. For example, she said, the word for "to haul" in Schwäbisch is schleppen, akin to the Yiddish shlepn שלעפּן , whereas standard German uses the more common schleifen. When I looked it up on Wikipedia, I found some more interesting similarities.
The diminutive ending "-le" (spoken very quickly, e.g. Haus may become Häusle, Bisschen may become Bissle) and "-la" for plurals (e.g. Spätzle becomes Spätzla). Wow. This is exactly like Yiddish (at least, the first part)! Hoyz הױז in the diminutive becomes hayzl הײַזל, and bisl ביסל is the Yiddish equivalent of standard German's Bisschen.
They always say that Swiss German is the closest form of German to Yiddish. What I didn't realize is that, as Wikipedia put it, "occasionally, the Alemannic dialects spoken in other countries are called Swiss German." Hmmm.