FRANKFURT—Bundesbank President Jens Weidmann, a relentless critic of the European Central Bank’s ultra easy monetary policy, will step down more than five years early, opening the door for Germany’s new government to pick a less confrontational successor. Weidmann said he would leave for personal reasons on Dec. 31, just days after the ECB must make a crucial decision on winding down pandemic-era stimulus that has revived growth but also pushed inflation to its highest rate in over a decade. Among the most conservative members of the ECB’s Governing Council, Weidmann often found himself in opposition to fellow euro zone policymakers during his decade heading the German central bank. He even warned about inflation risks in his farewell message to Bundesbank staff on Wednesday, saying: “It will be crucial not to look one-sidedly at deflationary risks, but not to lose sight of prospective inflationary dangers either.” The successor to Weidmann, a …