“I’ve made many wishes, but none have ever come true.” That line, written by a teenage girl in China’s remote Liangshan region, became the starting point for “Whispers in May,” the hybrid documentary by Emmy-nominated Chinese director Dongnan Chen (“14 Paintings,” “Singing in the Wilderness,” “Sound of Vision”), which will world premiere in the main competition at the Copenhagen Intl. Documentary Film Festival, also known as CPH:DOX . The doc – which Chen describes as a “reluctant coming-of-age