Jerry Lewis Freestyle Raps ... IN YIDDISH!!!

Jerry Lewis has mad Yiddish flow ... or maybe it's mad gibberish flow ... either way, it was definitely an attempt at a freestyle rap ... and TMZ has the footage.

The 87-year-old legend unleashed his skillz last week in between shooting scenes for his movie "Max Rose" -- when he injected himself into a rap battle with "America's Got Talent" sensation Chris La Vrar (who just happened to be on the set that day).

Lewis -- impressed with La Vrar's rhymes -- replied, "Very good. Very, VERY good ... I want to do one now in Jewish."

The crowd laughs -- but Jerry was SERIOUS -- and busts out a rap that you've just GOT to hear ... especially if you're a Yiddish scholar ... because then you can tell us what he says.

Seriously, we tried to make out the words ... but no dice.