Schlesien derived its name from the Silinger, a Germanic tribe like the Vandals and the (Celtic) Germanic Lugier or Lygier who all lived south of the Baltic Sea in the Elbe?, Oder, and Vistula river area. It should be noted that there is considerable debate among archaeologists and historians as to whether there is such a thing as a Celtic-Germanic people. Exhibits such as the one in Rosenheim (Bayern) certainly demonstrate that the Celts had an influence on the area; However, the movement of the Celts westward through Europe was such that there is little if any overlap between them and the Germanic tribes.
Moreover, the question of Germanic Tribes and their relationship to place names is entirely chicken/egg. Traditional German historiography, most notably the works of Ranke?, tend to argue a thing's inherent "Germanness" on the grounds that clearly work in a 19th century nationalist context, but hardly work for today's historians. To argue that the people living in Silesia when it was taken by the Slavs (AFTER it had been overrun by Vikings and others) were the same ethnic group as those living in Silesia in 1945 is insupportable.
Silesia was in earlier centuries overrun by Slavs. From 1945 it belongs to Poland. The Communists ousted most of the German population of Silesia. Some Geramans managed to stay in their homeland, while it was taken over by Poland, mainly in Opolskie voivoidship.
The Polish name today for Silesia is Slask?.
60 years later some book writers are finally heard at amazon.com on this Silent Ethnic Cleansing