Revert "remove lang fallback links"

This reverts commit 004d4d97f1.

app/templating/I18hHelper.scala

@@ -41,6 +41,13 @@ trait I18nHelper {
   def transValidationPattern(trans: String) =
     (trans contains "%s") option ".*%s.*"
 
+  def langFallbackLinks(implicit ctx: UserContext) = Html {
+    pool.preferredNames(ctx.req, 3).map {
+      case (code, name) => """<a class="lang_fallback" lang="%s" href="%s">%s</a>""".format(
+        code, langUrl(Lang(code))(I18nDomain(ctx.req.domain)), name)
+    }.mkString("").replace(uriPlaceholder, ctx.req.uri)
+  }
+
   private lazy val langAnnotationsBase: String =
     pool.names.keySet diff Set("fp", "kb", "le", "tp", "pi", "io") map { code =>
       s"""<link rel="alternate" hreflang="$code" href="http://$code.lichess.org%"/>"""
@@ -56,6 +63,9 @@ trait I18nHelper {
   def acceptLanguages(implicit ctx: UserContext): List[String] =
     ctx.req.acceptLanguages.map(_.language.toString).toList.distinct
 
+  def acceptsLanguage(lang: Lang)(implicit ctx: UserContext): Boolean =
+    ctx.req.acceptLanguages exists (_.language == lang.language)
+
   private val uriPlaceholder = "[URI]"
 
   private def langUrl(lang: Lang)(i18nDomain: I18nDomain) =

app/views/base/layout.scala.html

@@ -172,7 +172,11 @@ chessground: Boolean = true)(body: Html)(implicit ctx: Context)
           <a id="site_title" href="@routes.Lobby.home">
             lichess<span class="extension">.org</span>
           </a>
+          @if(acceptsLanguage(lang)) {
           @baseline
+          } else {
+          @langFallbackLinks
+          }
         </h1>
         @menu.map { side =>
         <div class="side_menu">@side</div>

public/stylesheets/common.css

@@ -567,6 +567,11 @@ strong {
 body.tight #site_header {
   display: none;
 }
+#site_header a.lang_fallback {
+  font-weight: bold;
+  display: inline-block;
+  margin-right: 1em;
+}
 body > div.content {
   width: 1005px;
   margin: 20px auto 30px auto;