Oliver Schmidt, a former Volkswagen manager in Michigan, was sentenced to seven years in prison for his role in the German automaker’s decade-long scheme to cheat on diesel emissions tests. He pleaded guilty to conspiracy to defraud the federal government and to violating the Clean Air Act. Most of those suspected of conspiring to defraud United States regulators are out of reach of American justice in Germany, which normally does not extradite its own citizens. Mr. Schmidt’s arrest in January, more than a year after the scandal erupted, was something of a fluke. Having been transferred back to Germany, he came to the United States for a vacation with his wife and was seized as he waited for a departing flight in Miami.