The NeutralResourcesLanguage attribute informs the ResourceManager of the language used to render the neutral culture's resources ...

The NeutralResourcesLanguage attribute informs the ResourceManager of the language used to render the neutral culture's resources for an assembly. When looking up resources in the same culture as the neutral resources language, the ResourceManager automatically uses the resources located in the main assembly, instead of searching for a satellite assembly with the current user interface culture for the current thread. This will improve lookup performance for the first resource you load and can reduce your working set.