This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
There is absolutely no need to worry about this message. If you're using internationaliztion in your application, you have the option of creating LocalStrings property files for each language you support. If you provide them, Struts validation will use them, but if you don't it will just use the default. Apparently your browser is set for US English, and because of this, Struts tried to find a US English specific properties file, and since it didn't find one, it used the default, which happens to be in English anyway.