I saw the film A Serious Man[0] at a cinema in Amsterdam when it came out. There's an opening scene with Yiddisch dialogue and it had no subtitles but judging from the laughs everyone understood it.
I‘m a run-of-the-mill West German dude with no particular talent for languages, and second this. It’s somewhere between “normal” German and Dutch in terms of understandibility for me.
I'm guessing the reason why is that the Jews migrated northwards from the Levantine / Africa / Spain upwards through Italy, Austria and then Germany, Poland, the Baltics.
Are there any Italian or Piedmontese / Venetian traces in Yiddish?
A lot of words and expressions in the old Viennese dialect are Yiddish, though that dialect has all but disappeared from day to day interactions (you can find it in old movies and recordings).