(legacy) fix some more php notices

src/www/head.inc

@@ -2,13 +2,13 @@
 
 function system_get_language_code() {
 	global $config;
+	$code = "en-US"; // Set default code.
 
 	// a language code, as per [RFC3066]
-	$language = $config['system']['language'];
-	$code = str_replace("_", "-", $language);
-
-	if (empty($code))
-		$code = "en-US"; // Set default code.
+	if (isset($config['system']['language'])) {
+		$language = $config['system']['language'];
+		$code = str_replace("_", "-", $language);
+	} 
 
 	return $code;
 }