TAIPEI, June 17 (Reuters) – Taiwan said on Wednesday it was up to U.S. President Donald Trump to decide when to follow through on a proposal to speak with Taiwan’s leader, adding that the idea made China nervous. Trump said following a summit with China’s Xi Jinping in Beijing last month that he would speak with Taiwan’s President Lai Ching-te. No U.S. president is known to have spoken to a leader of Taiwan since the United States recognised Chi…