I am trying to learn about WPF application. I was going very fine until I stopped at the level of making my application a multilingual one. for windows forms apps it was easier using a resource files and create and event to select the specified language according to the user selection. in WPF it seems very complicated (I don't know why) because all the solutions provided by individual programmers and they were complex and difficult to understand. No Microsoft formal involvement.
You should use WpfLocalizeExtension project. This project has good documentation.
If you want to build your own solution check this question: How to start an internationalized WPF-Project in SharpDevelop 4.2?