Well, since Yiddish and German exchanged words until the 1930s, they already share quite some similarities.
It's stunning if, as a German, one watches a TV show in English and one character starts talking Yiddish. Even though, it's then American-English-tainted Yiddish, one is wondering if the language setting changed or what's going on, since one can roughly understand half of it, plus a good amount more with the given context.