Add language switch to material itself.

Author: lehmannro

source/_templates/relations.html

@@ -14,3 +14,17 @@
     </a>
   </li>
 {%- endif %}
+<li class="dropdown">
+  <a role="button"
+     data-toggle="dropdown"
+     data-target="#"
+     href="#">{{ _('Languages') }} <b class="caret"></b></a>
+  <ul class="dropdown-menu"
+      role="menu">
+    <li><a href="../en/index.html">English</a></li>
+    <li><a href="../de/index.html">Deutsch (German)</a></li>
+    <li><a href="../es_CL/index.html">Español (Spanish)</a></li>
+    <li><a href="../ru/index.html">русский (Russian)</a></li>
+    <li><a href="../ko/index.html">한국인 (Korean)</a></li>
+  </ul>
+</li>