UNITED NATIONS — A former Nicaraguan foreign minister who once called President Ronald Reagan “the butcher of my people” has been appointed to represent Libya at the United Nations after its delegate was denied a visa, the Nicaraguan government said on Wednesday. Nicaragua said the former minister, Miguel D’Escoto Brockmann, 78, an outspoken critic of the United States and a Catholic priest, would replace the Libyan diplomat Ali Abdussalam Treki, who had been unable to obtain a visa to enter the United States. Libya’s ambassador to the United Nations, Abdurrahman Mohamed Shalgam, defected in late February after denouncing Col. Muammar...