S4026 — Assemblies should be marked with "NeutralResourcesLanguageAttribute"

Why is this an issue?

It is important to inform the ResourceManager of the language used to display the resources of the neutral culture for an assembly. This improves lookup performance for the first resource loaded.

This rule raises an issue when an assembly contains a ResX-based resource but does not have the System.Resources.NeutralResourcesLanguageAttribute applied to it.

Noncompliant code example

using System;

public class MyClass // Noncompliant
{
   public static void Main()
   {
      string[] cultures = { "de-DE", "en-us", "fr-FR" };
      Random rnd = new Random();
      int index = rnd.Next(0, cultures.Length);
      Thread.CurrentThread.CurrentUICulture = CultureInfo.CreateSpecificCulture(cultures[index]);

      ResourceManager rm = new ResourceManager("MyResources" ,
                                               typeof(MyClass).Assembly);
      string greeting = rm.GetString("Greeting");

      Console.Write("Enter your name: ");
      string name = Console.ReadLine();
      Console.WriteLine("{0} {1}!", greeting, name);
   }
}

Compliant solution

using System;

[assembly:NeutralResourcesLanguageAttribute("en")]
public class MyClass
{
   public static void Main()
   {
      string[] cultures = { "de-DE", "en-us", "fr-FR" };
      Random rnd = new Random();
      int index = rnd.Next(0, cultures.Length);
      Thread.CurrentThread.CurrentUICulture = CultureInfo.CreateSpecificCulture(cultures[index]);

      ResourceManager rm = new ResourceManager("MyResources" ,
                                               typeof(MyClass).Assembly);
      string greeting = rm.GetString("Greeting");

      Console.Write("Enter your name: ");
      string name = Console.ReadLine();
      Console.WriteLine("{0} {1}!", greeting, name);
   }
}