If you've ever studied the stories of the Jews you'll know a source of Jewish cohesiveness was their cross-border language: a Jew from Baghdad and a Jew from Marakesh both prayed in Hebrew and spoke Aramaic, and this facilitated commerce. Later, the Jew from Trier and the Jew from Krakow and the Jew from Tiberius, they all prayed in Hebrew, knew enough Aramaic to navigate the Talmud, and spoke Yiddish, and this, too, facilitated commerce. Still later, much later, Soviet officers liberating Nazi camps identified themselves to emaciated survivors with code words in Yiddish, though the Aramiac and Hebrew had mostly been lost in the turmoil of emancipation then Bolshevism. (The main problem the early Zionists had with the non-European Jews was that they didn't speak Yiddish).
One morning in the summer of 1981 I saw the end of this world. I was studying in Vienna at the time, and three young students from Belgium suddenly appeared at our shul for the morning service. The rabbi, an elderly man from Israel, greeted the new comers in the time-honored tradition, asking them in Yiddish where they were from and if they needed anything. They looked discomfited, and responded in Hebrew.
That was thirty years ago. The elderly rabbi has long-since passed on, as has his generation and the remnants of his world; the students of that morning are middle-aged men. Earlier today I called the Chabad (Lubavitch) house in an Italian town where I'll be spending next weekend, to ask about some arrangements. The fellow who picked up the phone spoke perfect Hebrew, the obvious language for Jews of different lands to communicate in.