During many years, the German colonies and the native Brazilians didn’t interact with each other. This caused that the German descendants didn’t know how to speak Portuguese.
This was a problem after World War Two because the German descendants were hunted and killed by the Brazilians because many of them were Nazis, and Brazilians were afraid that the rest would become Nazis too. After the massacre ended, the colonies were temporarily prohibited of speaking German or it derivatives, so they were forced to learn Portuguese. At that moment this was a horrible act were many people suffered, but this later led to some positive results, such as the bigger interaction between the cultures and the increase of the combination of traditions between both cultures. Nowadays, German descendants are completely allowed to speak German dialects.
Geography Genius Project: German Colonies in Brazil 