Explanation of the changes:
1) There was revert war over Gdansk/Danzig. Danzig (Gdansk) is a compromise which was supposed to stop such revert war (ridiculous: take a look on  article history. It is article about Polish-German painter, yet the last 50 changes were edits changing Gdansk to Danzig and vice versa
2) Danzig is nt just German name. It's also name by which still the city is known in English world, although the fact probably will change in the future. Therefore it's reasonable to mention both names
3) There is no such case, i believe, with Frauenburg. It's small city so there is no point in making alternative name too.