Most Asian currencies weakened slightly on Wednesday as the dollar rose from a near four-year low. This move comes ahead of the Federal Reserve's interest rate decision, which is widely expected to leave rates unchanged at 3.75%. The Japanese yen has benefited the most from recent dollar weakness, but speculation of currency market intervention by Tokyo has also boosted the yen.

The Australian dollar retreated from a near three-year high after hotter-than-expected December inflation data. This increase has ramped up bets on a rate hike by the Reserve Bank of Australia. Analysts are split on whether further hikes will follow, but the general consensus is that a 25 basis points hike is likely next week.

The dollar's recent weakness has been attributed to uncertainty over the U.S. economy and President Donald Trump’s policies. Focus is now on Fed Chair Jerome Powell's comments during the upcoming meeting. Trump has hinted at replacing Powell and has criticized his leadership, adding to the market's uncertainty.

The Chinese yuan and Indian rupee showed mixed performances, with the yuan reaching a 31-month low despite recent support from Beijing. The rupee, meanwhile, remained above 91 rupees, close to a record high, reflecting broader economic uncertainties in India.