In the case of buing yuan

China has been buying it's currencies while it may in the short run increase it's value against dollar, the underlying issue with yuan is the fundamentals of chinese commerce has yet to change.

Property investment still not resolved in the case where it is expensive but there is no demand for the number of supply.

Failure to pay debts.

Aggressive actions against her neighbors by invading the terrirtorial watters of other countries.

Using debt to control other neighbors.

Dollar is king.

Yuan challenging the dollar is still a pipe dream.