Chinese authorities have weakened the yuan’s midpoint against the US dollar for a third trading day, despite the European Central Bank chief joining a chorus highlighting the supposed undervaluation of the Chinese currency.The People’s Bank of China set the yuan’s midpoint rate – which guides onshore market trading within a 2 per cent band on the up and down sides – at 6.8195 per US dollar, compared with 6.8171 on Tuesday.A three-year high was set 6.8088 on June 15, buoyed by the easing of...