China's plans for a tax on currency trading triggered an outcry of criticism about the potential hit to financial markets. Obscured in the conversation is how the move shows again that the world's No. 2 economy isn't content with acceding to a global financial system crafted by No. 1.

No major economy has implemented a Tobin tax, a move that backers say would curb currency speculation that distorts exchange-rate values. The rules still need central government approval, and it's not clear how quickly they can be implemented, according to people familiar with the matter. The initial levy would be kept at zero to allow authorities time to refine the rules, and it wouldn't be designed to disrupt hedging and other foreign-exchange transactions undertaken by companies, they said.

One hope: A Tobin tax could help curb an outflow of funds from China that last year reached a record $1 trillion. The idea follows China's use of its leadership of the Group of 20 to examine proposals that would reduce the dollar's dominance. Other evidence of China's desire to revamp global financial architecture has been seen in its launch of development banks to rival established lenders such as the World Bank.