from the link: during WWII, my father-in-law was in the American army, in one of the advance units moving into Germany. He was the translator when his unit encountered German civilians, because he spoke Yiddish--as close to German as his unit was going to get.

When my parents traveled in Europe (not Germnany) in the 1960's and would try to communciate with folks who spoke no English, they quickly discovered that my mother's french was far less useful than my father's yiddish.