Generate Umbraco Sitemap with HREF Lang tags

GenerateUmbracoSitemap.cs

 public static byte[] GenerateSiteMap(IPublishedContent model)
{
    var sites = model.Parent.Children.Where(x => x.DocumentTypeAlias == "HomePage" || x.DocumentTypeAlias == "SatelliteHomePage");

    var baseUrl = string.Format("{0}://{1}", HttpContext.Current.Request.IsSecureConnection ? "https" : "http", HttpContext.Current.Request.Url.Host);

    var siteMap = new XmlSiteMap();

    foreach (var homePage in sites)
    {
        siteMap.Urls.Add(GetPage(baseUrl, homePage));
        siteMap.Urls.AddRange(GetChildPages(homePage, baseUrl));
    }

    // create xml feed
    XNamespace xmlns = "http://www.w3.org/1999/xhtml";
    XNamespace sitemapns = "http://www.sitemaps.org/schemas/sitemap/0.9";

    var xdoc = new XDocument(
        new XDeclaration("1.0", "UTF-8", null),
        new XElement(sitemapns + "urlset",
            new XAttribute("xmlns", "http://www.sitemaps.org/schemas/sitemap/0.9"),
            new XAttribute(XNamespace.Xmlns + "xhtml", "http://www.w3.org/1999/xhtml")
        )
    );

    for (int i = 0; i < siteMap.Urls.Count; i++)
    {
        var doc = siteMap.Urls[i];

        var item = new XElement(sitemapns + "url");

        item.Add(new XElement(sitemapns + "loc", doc.Url));
        item.Add(new XElement(sitemapns + "lastmod", doc.Modified));

        if (doc.Alternates != null && doc.Alternates.Any())
        {
            foreach (var alt in doc.Alternates)
            {
                if (alt.Lang != null && alt.Url != null)
                    item.Add(new XElement(xmlns + "link", new XAttribute("rel", "alternate"), new XAttribute("hreflang", alt.Lang), new XAttribute("href", alt.Url)));
            }
        }

        xdoc.Root.Add(item);
    }

    using (var ms = new MemoryStream())
    {
        using (var sw = new StreamWriter(ms, Encoding.UTF8))
        {
            xdoc.Save(sw);
            return ms.ToArray();
        }
    }
}