plainui: language selector: use direct link in archive_mode

src/plainui/jinja2/plainui/components/header_buttons.html

@@ -52,6 +52,7 @@
     </svg>
   </a>
   <ul class="dropdown-menu dropdown-menu-end" aria-labelledby="lang-select">
+    {% if not archive_mode %}
     <form
         class="hub-header__additional-lang"
         method="POST"
@@ -74,6 +75,10 @@
             {{ _("en") }}
         </button></li>
     </form>
+    {% else %}
+      <li><a class="dropdown-item" href="{{ hub_absolute_self(request, lang='de') }}">{{ _("de") }}</a></li>
+      <li><a class="dropdown-item" href="{{ hub_absolute_self(request, lang='en') }}">{{ _("en") }}</a></li>
+    {% endif %}
   </ul>
 {%- endmacro %}