Czech lands are a place where many different language elements meet - there si Czech language, but there were parts where German was the most common language till the half of the 20th century. How did this happen?
As you most probably know, one third of the Czech lands inhabitants were Germans till the second half of 1940s. This was caused by the large medieval colonisation when owners of Czech estates invited people from quite overcrowded Bavaria and other German speaking regions to come and settle in almost uninhabited regions of Bohemia, Moravia and Silesia. As these people were living in quite secluded areas (such as mountain valleys) they kept their language and spoke German.