Post_12_1.cs

public class RouteValueRequestCultureProvider : RequestCultureProvider
{
  public override Task<ProviderCultureResult> DetermineProviderCultureResult(HttpContext httpContext)
  {
    string cultureCode = null;

    if (httpContext.Request.Path.HasValue && httpContext.Request.Path.Value == "/")
      cultureCode = this.GetDefaultCultureCode();

    // TODO: make it look more beautiful
    else if (httpContext.Request.Path.HasValue && httpContext.Request.Path.Value.Length >= 4 && httpContext.Request.Path.Value[0] == '/' && httpContext.Request.Path.Value[3] == '/')
    {
      cultureCode = httpContext.Request.Path.Value.Substring(1, 2);

      if (!this.CheckCultureCode(cultureCode))
        cultureCode = this.GetDefaultCultureCode(); //throw new HttpException(HttpStatusCode.NotFound);
    }

    else cultureCode = this.GetDefaultCultureCode(); //throw new HttpException(HttpStatusCode.NotFound);

    // TODO: from the SEO point of view, we should return 404 error code for unknown cultures

    ProviderCultureResult requestCulture = new ProviderCultureResult(cultureCode);

    return Task.FromResult(requestCulture);
  }

  private string GetDefaultCultureCode()
  {
    return this.Options.DefaultRequestCulture.Culture.TwoLetterISOLanguageName;
  }

  private bool CheckCultureCode(string cultureCode)
  {
    return this.Options.SupportedCultures.Select(c => c.TwoLetterISOLanguageName).Contains(cultureCode);
  }
}