if (cookieLang == null)
            {
                cookieLang = new HttpCookie("Language");
            }
            cookieLang.Value = "ru-RU";
            cookieLang.Expires = DateTime.Now.AddDays(1);
            Response.Cookies.Add(cookieLang);
            Response.Redirect(Request.Path);

            if (HttpContext.Current.Request.Cookies["Language"] != null)
            {
                HttpCookie cookie = HttpContext.Current.Request.Cookies["Language"];
                string lang = cookie.Value;
                var culture = new System.Globalization.CultureInfo(lang);
                Thread.CurrentThread.CurrentCulture = culture;
                Thread.CurrentThread.CurrentUICulture = culture;
            }

<globalization  culture="ru-RU" uiCulture="ru-RU" />
или
<globalization  culture="en-US" uiCulture="en-US" />

                Thread.CurrentThread.CurrentCulture = culture;
                Thread.CurrentThread.CurrentUICulture = culture;