Localizing a Silverlight application is a pretty trivial task if you use resources.  Once you create a resource file you are working with, you can use the code-behind class in XAML and bind to properties from that class that contain localized strings.  First, import the namespace that is used for resx file, typically ApplicationResources

xmlns:Localized="clr-namespace:MyApplication.Resources"

Then add an instance of a specific resx code-behind class to resources in your user control

<UserControl.Resources>
    <Localized:SpecificFile x:Name="LocalizedStrings"/>

In this case SpecificFile corresponds to SpecificFile.resx.  Now that this is done, you can bind labels to it

<TextBlock Text="{Binding Path=MyPropertyFromResourceFile}/>

There is one issue though, if you edit resource file again in resources editor, and save it, the constructor scope in code behind is set to internal.  This in turn will cause an exception (AG_E_PARSER_UNKNOWN_TYPE  ) when you try to load this user control.  All you have to do to fix it is edit code behind file for you resource file and change its constructor to public.  Unfortunately, you have to do it every time you edit the file in resources editor.