Umbraco : on root node, redirect to current users browser culture ex: /en/ or /fr/

RedirectToLanguage.cshtml

@using System.Globalization
@inherits Umbraco.Web.Mvc.UmbracoTemplatePage
@{
    Layout = null;

    string[] languages = HttpContext.Current.Request.UserLanguages;
    var detectedLanguage = false;
    var urlToRedirect = "/en/";  // TODO : go to first node homepage?

    if (languages != null && languages.Any())
    {
        var allHomapeges = Model.Content.Descendants("Homepage");

        if (allHomapeges != null && allHomapeges.Any())
        {
            foreach (var lang in languages)
            {
                if (detectedLanguage)
                {
                    break;
                }

                var letfLanguageTag = CultureInfo.GetCultureInfoByIetfLanguageTag(lang.Split(';')[0]).IetfLanguageTag;

                @* <div>@lang » @letfLanguageTag</div> *@ // DEBUG

                foreach (var homepage in allHomapeges)
                {
                    if (homepage.Name.Equals(letfLanguageTag, StringComparison.InvariantCultureIgnoreCase))
                    {
                        urlToRedirect = homepage.Url;
                        detectedLanguage = true;
                        break;
                    }

                    if (detectedLanguage)
                    {
                        break;
                    }
                }
            }
        }
    }

    Response.RedirectPermanent(urlToRedirect);  // DONT END RESPONSE
}

More info in my blog
http://adaodeveloper.blogspot.pt/2016/04/umbraco-redirect-root-node-to-users.html