[ticket/9970] User language input is checked for existance

Users could select a language which did not exist in the database by altering
form fields because there was no back-end verification.

PHPBB3-9970

phpBB/includes/ucp/ucp_prefs.php

@@ -65,7 +65,7 @@ class ucp_prefs
 
 					$error = validate_data($data, array(
 						'dateformat'	=> array('string', false, 1, 30),
-						'lang'			=> array('match', false, '#^[a-z0-9_\-]{2,}$#i'),
+						'lang'			=> array('language'),
 						'tz'			=> array('num', false, -14, 14),
 					));