I had a little bit of difficulty messing around getting the ResourceManager the class generated when making a resource file (resx). I wanted to get the value of something using a string and do it by accessing the ResourceManager property and calling the GetString() method myself. This is what i used to get the resource manager
Note you will need to make the resource file public if referencing as resource file in another assembly.
// Get the ResourceManager on the type
var resourceManager = (ResourceManager)ResourceType.GetProperty("ResourceManager",
System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Static).GetValue(ResourceType, null);
// Get information on the getstring method
return resourceManager.GetString(_resourceKey, CultureInfo.CurrentCulture);