FRANKFURT — When Wolfgang Schäuble, the German finance minister and war horse of European politics, celebrated his 70th birthday at a theater in Berlin last September, two of the most powerful women in the world offered warm words in his honor. One was Chancellor Angela Merkel. The other, delivering the keynote speech, was …more, the managing director of the . Ms. Lagarde’s presence reflected her close, longtime friendship with Mr. Schäuble. But it also was a confirmation of the enormous stature that Ms. Lagarde and the I.M.F. have acquired in Europe as a result of the euro crisis.