Boris Johnson’s political comeback as U.K. foreign secretary sparked reactions from surprise to dismay among officials around the world, many of whom see him as the symbol of his country’s disruptive decision to leave the European Union.

A number of foreign officials have blamed Mr. Johnson, a provocative former newspaper columnist and ex-mayor of London, for much of the venomous discourse about Europe that dominated the Brexit campaign. They painted his decision to drop out of the race to succeed David Cameron as prime minister...