An assembly contains a ResX-based resource but does not have the System.Resources..::.NeutralResourcesLanguageAttribute applied to it.

The NeutralResourcesLanguage attribute informs the ResourceManager of the language that was used to display the neutral culture's resources for an assembly. When it looks up resources in the same culture as the neutral resources language, the ResourceManager automatically uses the resources that are located in the main assembly. It does this instead of searching for a satellite assembly with the current user interface culture for the current thread. This improves lookup performance for the first resource you load and can reduce your working set.

To fix a violation of this rule, add the attribute to the assembly, specifying the language of the neutral culture's resources.

To specify the language of the neutral culture’s resource

It is permissible to suppress a warning from this rule. However, startup performance might decrease.