NeutralResourcesLanguageAttribute is Evil for ResourceFiles
Two Resource files named Strings.resx and Strings.de.resx.
The first (neutral) contains english content, the second german content.
If you ask youself over and over again why the f**k the ResourceManager returns the neutral language even you use the specified language “de”, look into your AssemblyInfo.cs file.
If there is a [assembly: NeutralResourcesLanguage("de")], the ResourceManager from this Assembly thinks you want to get the neutral language if you ask for “de” explicit.
This attribute is used to overrule the neutral settings to a specific one.
Deleting this from your AssemblyInfo.cs can help you realy much in this case.