The NeutralResourcesLanguageAttribute informs the resource manager of the language that was used to display resources which are contained in the main assembly. E.g. if you coded your assembly so that it contains resources which are in English, then include the following line in your AssemblyInfo.cs
[assembly: NeutralResourcesLanguage("en")]
This way, when looking up resources in English, the resource manager will not look for an English culture satellite assembly, but rather just use the resources contained in the main assembly. This is purely a performance optimisation.