Silverlight localization (.xap files)
Lingobit Localizer can be used for Silverlight localization (.xap).
The .xap file contains an application manifest (AppManifest.xaml) file and all the necessary DLL's that are required by the application. The first DLL contained is the compiled version of you application and has the same name of your application. In my test I created an application names "SilverlightApplication1", so the DLL is named "SilverlightApplication1.dll". The rest of the DLL's are the dependancies the application requires.
How it works
Therefore, for Silverlight localization you need to unpack Silverlight .xap file, localize packed files and then pack it back again. Files inside .xap are usual WPF and .NET assemblies. You can read about it at WFP localization and .NET localization.
In future version we plan to add support for localization of .xap files, that will do pack and unpack operations automatically.
Other .NET localization platforms
.NET Framework has several technologies that use slightly different approaches for localization. Please select the one you need