HONG KONG—British judge Brenda Hale will step down from Hong Kong’s Court of Final Appeal next month when her three-year term expires, the judiciary said on Friday, a move that may deepen uncertainty over the role of foreign judges in the semi-autonomous city. The departure of Hale, a former president of Britain’s Supreme Court, comes amid international concern over the effect on the city of a national security law imposed by China’s parliament a year ago. Diplomats and business people say the law’s impact on Hong Kong’s independent judges and separate legal system is being particularly closely watched given their importance to its status as a global financial hub. Hale is one of 13 overseas non-permanent judges on the top court—a presence that has long been seen as a symbol of the rule of law after Britain handed the former colony back to China in 1997. The Hong Kong Judiciary …