יידיש
Yiddish
Norwood +1Yiddish, the principal mother tongue of European (or Ashkenazi) Jews, has likely been spoken in the city since the 17th century, but large waves of speakers first arrived in the 19th century: initially German Jews, some of whom apparently still used now largely moribund Western Yiddish, and later large numbers of speakers of all varieties of Eastern Yiddish from across Yiddish-speaking Eastern Europe. By the early 20th century, New York City had become the largest Yiddish-speaking center in the world, with mass media, theater, and other institutions to match.
T
he Bronx became a major new area of settlement for Jews leaving the Lower East Side in the 1920s and 1930s, with the more prosperous clustering around the Grand Concourse and more working-class people in the South or East Bronx. Many neighborhoods remained substantially Yiddish speaking, with Yiddish theaters, schools, and a rich institutional life. Shift to English usually came within a generation or two, though some avowed Yiddishists worked to maintain language at key sites, including on Bainbridge Avenue in the Bronx where the "Bainbridgivke" community formed in the 1960s and some speakers still gather today.
Note that the language above may be used throughout the New York area — this is just one significant site.