diff --git a/install/lang/az/langconfig.php b/install/lang/az/langconfig.php
index a96efd86283..71b23d234ec 100644
--- a/install/lang/az/langconfig.php
+++ b/install/lang/az/langconfig.php
@@ -29,5 +29,7 @@
 
 defined('MOODLE_INTERNAL') || die();
 
+// Warning: this parentlanguage value is not a valid language code!
+// $string['parentlanguage'] = '_';
 $string['thisdirection'] = 'ltr';
 $string['thislanguage'] = 'Azərbaycanca';