Setup dlfmwiki for system messages' translation. (#5346)

As previously mentioned in
[T11314](https://phabricator.miraheze.org/T11314), I need to add these
configurations for my wiki to setup system translation.

LocalWiki.php

@@ -35,6 +35,17 @@ function onSkinAddFooterLinks( Skin $skin, string $key, array &$footerItems ) {
 			}
 		}
 
+		break;
+	case 'dlfmwiki':
+		$wgHooks['TranslatePostInitGroups'][] = function ( &$list, &$deps, &$autoload ) {
+			$id = 'local-sys-msg';
+			$mg = new WikiMessageGroup( $id, 'local-messages' );
+			$mg->setLabel( 'Local System Messagss' );
+			$mg->setDescription( 'Messages used specially on this wiki.' );
+			$list[$id] = $mg;
+			return true;
+		};
+
 		break;
 	case 'dmlwikiwiki':
 		$wgHooks['SpecialPage_initList'][] = 'onSpecialPage_initList';