The approach that I described in the following article to use a single satellite Dll with the “en-US” culture using the AppDomain.AssemblyResolve event doesn’t work in VS 11 Beta:

HOWTO: Create a command with a custom picture using a managed satellite DLL for a XML-based Visual Studio add-in.
http://www.mztools.com/articles/2012/MZ2012002.aspx

I have just opened a bug report at Microsoft Connect:

VS11 Beta does not raise AppDomain.AssemblyResolve to receive the satellite dll in add-ins in localized versions
https://connect.microsoft.com/VisualStudio/feedback/details/731914/vs11-beta-does-not-raise-appdomain-assemblyresolve-to-receive-the-satellite-dll-in-add-ins-in-localized-versions#details

BTW, some other bugs that I have been reporting will be fixed in next builds of VS 11, according to the Microsoft answers. Hopefully this is fixed too.