Both the onshore and offshore yuan breached the 7.0 level against the dollar, which investors see as a key threshold in currency value China's decision to let its currency weaken against the dollar on Monday sent global markets diving further into the red and provoked a Twitter tirade from US President Donald Trump. The deteriorating picture appeared to worsen as official Chinese media reported Beijing ceased purchases of American farm exports. The Chinese yuan fell to its lowest level against the dollar since August 2010 in morning trading on Monday, fuelling speculation that Beijing is allowing currency depreciation to counter...