Recently, a customer checked out through my POWr eCommerce Plugin, and PayPal appeared in Chinese. What's going on?
Don't panic! The problem is not with your eCommerce Plugin.
Sometimes, if a shopper visits a foreign website or purchases something from another country, a cookie will be left on their machine. This cookie can tell the browser to load particular webpages in that foreign language the next time they are viewed.
Your customer probably purchased something from a Chinese retailer recently, and is seeing pages render in Chinese as a result.
Here's an article from the PayPal Community Forum about incorrect languages displaying in PayPal.