History until 1919 South Tyrol was part of Austria, after the peace treaty of St. Germain it became part of Italy. The language used in ST was 100% Austrian German. In 1939 the population of ST was offered by Hitler to return to the Reich quiet a lot declined. The Tyrolians were actually hoping to return South Tyrol to Austria but Hitler and Mussolini had other plans. Only after WWII did South Tyrol have a larger italian speaking population. Even tough the majority of todays STyrolians speaks italian there is still a large separatist movement. And most of the South Tyroleans are bilingual.