A former colleague who speaks German fluently gave me to believe that French is now the dominant language in that region. (He was stationed nearby in Germany when in the Army and used to have study abroad classes which used Strasbourg as their base.)
Germans understandably did not like the territorial losses after the war. But if they had won they were planning to annex territory from their defeated enemies. I don't think they were justified in starting World War II because of the Treaty of Versailles.
Czecho-Slovakia is often held up as an admirable state among the new states formed after 1918, but I think it was not only the Germans but also the other non-Czech ethnic groups who were not entirely happy with how the Czechs ran the country. The reason for assigning the Sudetenland to the Czechs was to give the country a defensible border. After the Munich agreement in 1938, the remainder of Czecho-Slovakia was defenseless against Germany.
They were fully fledged French citizens yes. But there were issues about the French discriminating against the use of their local dialect (something France did with others like the Bretons and the Corsicans too). Also, a strictly secular state to the point of being anti clerical, that too was not liked very much in Elsass Lothringen. So yes, it wasn't terrible for them being part of France but those things ended when Germany took the province back so they were just fine with being part of Germany again.
It was no more foolish of Bismarck to demand the province back than it was for the French to take it in the first place. The French acted butt-hurt ever afterward but they were always going to do that given their wounded pride at having lost. Remember, France was THE dominant power on the Continent for quite some time. Then Germany reunified and defeated them in a war while doing so. Their pride was severely wounded.
The Germans did claim territory from Russia in the Treaty of Brest-Litovsk that ended Russia's participation in WWI. Of course, the other side of the argument is that Germany couldn't feed itself and the British naval blockade led to the deaths of about 700,000 German civilians during the war due to starvation and they needed more farmland to feed their population. So....greedy in seizing territory? Arguably yes. What would you have done if you were watching your people being starved? I'd call their demand for land from Russia in light of that understandable.
I don't think the Germans were justified in starting WWII and would not support that argument. You are correct that other minority nationalities like the Hungarians and the Poles also did not like being oppressed minorities in the newly created Czechoslovakia which was Czech dominated. Did you know that when Hitler seized the Sudetenland for Germany, Poland and Hungary also reclaimed and took back bits of territory from Czechoslovakia? It happened. A lot of historians don't like to talk about it because well.....its very inconvenient for the narrative that it was all and only Germany that had a problem with the newly created Czechoslovak state.
I'm aware that they gave the Sudetenland to Czechoslovakia to make it more militarily defensible, but the locals were not Czechs and didn't want to be part of a Czech dominated state. Do other countries get to claim swathes of land filled with people who are not their own because that land would be useful to them too....or is that a privilege only to be extended to the Czechs?....or only when it would screw over Germans?