Location of custom language file

I am adding language changes to a custom language file
application/language/english/custom_lang.php

But I see the file is being looked for here :
vendor/codeigniter/framework/system/language/english/custom_lang.php

Am I missing something to get it to look in the application directory?

I found a workaround by changing
application/helpers/trans_helper.php

function set_language($language)
     // Set the new language
     $CI->lang->load('ip', $new_language);
     $CI->lang->load('form_validation', $new_language);
-    $CI->lang->load('custom', $new_language);
     $CI->lang->load('gateway', $new_language);
 }

change to

function set_language($language)
     // Set the new language
     $CI->lang->load('ip', $new_language);
     $CI->lang->load('form_validation', $new_language);
     $CI->lang->load('custom', $new_language, false, true, APPPATH);
     $CI->lang->load('gateway', $new_language);
 }

I’ll add a pull request for this change.