Mention must…be made of another new dialect that came about in the twentieth century: Chareidi Yeshivish Hebrew. This dialect, which evolved after the Holocaust, both in Israel and America, is a blend of the Lithuanian and Polish pronunciations, which ironically enough originated with the Yiddishists. In the early part of the twentieth century, the Yiddishists set out to standardize Yiddish pronunciation by combining elements of Lithuanian and Polish pronunciation of Yiddish. This pronunciation was subsequently adopted by the Yeshivish community. Of course, no one from Slabodka, Radin, Mir, Lublin, Pressburg or Satmar ever used this dialect in Europe.
Seth Mandel, “The Real Story of Hebrew Pronunciation”, Jewish Action (Spring 2014), 18.