In this article, Suprotim Agarwal demonstrates how to localize a Silverlight 4 application.
Source: Dot Net Curry
In simple words, localization is the customization of applications for a given culture or locale. If you have been doing ASP.NET development, you probably are already familiar with localizing applications. The process of localizing a Silverlight application is quite similar, i.e. using Resource files. You create a resource file for each culture or language your application plans to support and Silverlight will use the CurrentUICulture of the UI thread to decide which resource to use. Let us see the steps in detail.