No, they didn't take Elsass-Lothringen. They took most of Elsass, the eastern part of said area. And there was a reason why the Germans had much nationalist ambitions about Elsass, namely the Elsässich.The First Reich? All I can say is, why? The Germans took Alsace Lorraine from France to form the Reich. Please don't argue it was originally German, that was before the age of nationalism.
Considering what the Germans would have done to the Poles if they had won.....
By the way, Gdansk was always a Polish speaking city,as was/is (1st Reich held) Posen. Going by your logic in regards to German ownership of Alsace, these former territories that were "stolen" by Prussia ought to be reffered to by their Polish names.
And no, Danzig weren't always a Polish speaking city. That city changed demographically quite a lot during it's history! In fact, in the 20s and 30s, Danzig had a majority German population (the entire area between Germany proper and East Prussia didn't, but neither did it have a majority Polish population, at that).