Change website language based on DropDownList selection using C# in ASP.Net

I have a site with login page. In that page i placed a dropdownlist that have 3 language I can change the second and third language in the dropdownlist but not the first I use cookie so in the login.aspx and basePage(inherit from System.Web.UI.Page)

<asp:DropDownList ID="ddlLanguages"  
 runat="server" 
 AutoPostBack="true" 
 OnSelectedIndexChanged="ddlLanguages_SelectedIndexChanged">
                  <asp:ListItem Text="Ita" Value="it-IT" /> 
                  <asp:ListItem Text="Eng" Value="en-US" />
                  <asp:ListItem Text="Esp" Value="es-AR" />
               </asp:DropDownList>

protected void ddlLanguages_SelectedIndexChanged(object sender, EventArgs e) 
{
 HttpCookie language = new HttpCookie("UserLanguage");
switch (ddlLanguages.SelectedItem.ToString())
{
case "Ita": 
language.Values["UserLanguage"] = "it-IT";
break;
case "Eng": 
language.Values["UserLanguage"] = "en-US";
break;
case "Esp": 
language.Values["UserLanguage"] = "es-AR";
break;
default:
break;
}

language.Expires = DateTime.Now.AddDays(1);
Response.Cookies.Add(language);
}

In the BasePage (BasePage : System.Web.UI.Page):

protected override void InitializeCulture()
    {      
        String userLang = "";  
        if (Request.Cookies["UserLanguage"] != null)
        {
            HttpCookie CookieKey = Request.Cookies["UserLanguage"];
            String cookieValue = CookieKey.Value.Split('=')[1];
            switch (cookieValue)
            {
                case ("it-IT"):
                    userLang = cookieValue;
                    break;
                case ("en-US"):
                    userLang = cookieValue;
                    break;
                case ("es-AR"):
                    userLang = cookieValue;
                    break;
            }

            Thread.CurrentThread.CurrentCulture = new CultureInfo(userLang);
            Thread.CurrentThread.CurrentUICulture = new CultureInfo(userLang);
        }
        else
        {
            userLang = "it-IT";
            Thread.CurrentThread.CurrentCulture = new CultureInfo(userLang);
            Thread.CurrentThread.CurrentUICulture = new CultureInfo(userLang);
        }

    }

I can set Es and then En but not Es (or En) and then It . Why ?