Set party lang as a configuration option

configuration.xml

@@ -11,6 +11,8 @@ this repository contains the full copyright notices and license terms. -->
                 <form string="Party Configuration">
                     <label name="party_sequence"/>
                     <field name="party_sequence"/>
+                    <label name="party_lang" />
+                    <field name="party_lang" widget="selection" />
                 </form>
                 ]]>
             </field>