In 1939 East Prussia had 2.49 million inhabitants, 85% of them ethnic Germans, the others Poles in the south who, according to Polish estimates numbered in the interwar period around 300,000-350,000, the Latvian speaking Kursenieki, and Lietuvininkai who spoke Lithuanian in the northeast. Most German East Prussians, Masurians, Kursieniki, and Lietuvininkai were Lutheran, while the population of Ermland was mainly Roman Catholic due to the history of its bishopric. The East Prussian Jewish Congregation declined from about 9,000 in 1933 to 3,000 in 1939, as most fled from Nazi rule. Those who remained were later deported and killed in the Holocaust.
What language did ethnic Germans mostly speak?