When the Chinese currency (CNY) suddenly plunged in the middle of August 2015, a stunned world conditioned by decades of econometrics condemned China for its brazenness. Currency exchange rates are set, we are told, by learned experts conducting predetermined policies. Therefore, an abrupt devaluation like that one must have been an intentional change in strategy.
In the face of growing economic weakness, the masters of CNY were purportedly undertaking export stimulus. Lower the currency, make the goods you produce a bit cheaper on global markets, voila, economic acceleration. It's in all the textbooks.