I have a simple Windows Phone 8 (WP8) app which I have localized by modifying AppResources.resx to create a version for Spanish.
Problem is the \'Application Title
I have followed the "How to localize an app title for Windows Phone", downloaded the "Language-Neutral Resource Project" and succeeded in localizing my app's title. Note: in "Language-Neutral Resource Project", you have to replace the "#include "afxres.h" by "#include "winnt.rh"", and delete all included libraries in "Properties > Linker > Input > Additional Dependencies". Good luck!
I had to place the AppResLib.dll.{lang}.mui in the root folder and not in "Resources" as asked by the MS tutorial. (Double check in the file properties that the Build Action is "content")
May I also suggest this tool: WP7 AppResLib DLL Generator. It will help you generate the localized dlls out of an XML file. This is especially useful if you are using the express edition of Visual Studio. The tool was initially built for WP7, but it is also working for WP8.
I would also like to raise your attention to this thread. You may experience the same issue that the localized app title appears correctly on the tiles, but on the store. The solution to this is to use specific language codes (en-US, de-DE) and completely avoid generic ones (en, de).