Multilingual App toolkit for Visual Studio 2012 helps the windows Phone and Windows store app developers to integrate Multi lingual/localization capability in your applications.
This extension for Visual Studio 2012 helps you localize your Windows Store and Windows Phone apps with translation support, translation file management, and editor tools.
Download Multilingual App Toolkit for Visual Studio 2012
read the Blog from windows Phone team for more details: tips for localizing windows phone apps
See some related videos here: