Trigger warning with missing lang strings

required.php

@@ -136,6 +136,7 @@ function lang($key, $echo = true) {
     if (array_key_exists($key, STRINGS)) {
         $str = STRINGS[$key];
     } else {
+        trigger_error("Language key \"$key\" does not exist in " . LANGUAGE, E_USER_WARNING);
         $str = $key;
     }
 
@@ -158,6 +159,7 @@ function lang2($key, $replace, $echo = true) {
     if (array_key_exists($key, STRINGS)) {
         $str = STRINGS[$key];
     } else {
+        trigger_error("Language key \"$key\" does not exist in " . LANGUAGE, E_USER_WARNING);
         $str = $key;
     }