[plg_system_stats] Load plugin language files only when needed (#11728)

* Load plugin language files only when needed (if plugin enabled and user in administrator client)

* Update stats.php

* remove autoloadLanguage property and use this

plugins/system/stats/stats.php

@@ -43,14 +43,6 @@ class PlgSystemStats extends JPlugin
 	 */
 	protected $app;
 
-	/**
-	 * Load plugin language files automatically
-	 *
-	 * @var    boolean
-	 * @since  3.5
-	 */
-	protected $autoloadLanguage = true;
-
 	/**
 	 * Database object
 	 *
@@ -99,6 +91,9 @@ public function onAfterInitialise()
 			return;
 		}
 
+		// Load plugin language files only when needed (ex: they are not needed in site client).
+		$this->loadLanguage();
+
 		JHtml::_('jquery.framework');
 		JHtml::script('plg_system_stats/stats.js', false, true, false);
 	}