Yiddish - a mixture of Hebrew and Middle German, spiced with Aramaic, Greek, Latin, Old French and Old Italian, was once spoken by more than ten million people - nearly two thirds of the world's entire Jewish population.
It has suffered a dramatic decline over the last century.
Dennis Marks continues his investigation in New York.
He meets Aaron Lansky, founder of the National Yiddish Book Centre, a library dedicated to rescuing and saving Yiddish books - as he says - from the dustbin of history.
The Centre has saved and preserved thousands of books, many of which now reside in libraries in Oxford, in an attempt to keep this joyful, exuberant language alive.