On account creation, the message is not displayed I try to register in my site; after a successful registration, I get redirected to the home page, but the following message is not displayed.


  Thank you for applying for an account. Your account is currently pending approval by the site administrator.
  
  In the meantime, a welcome message with further instructions has been sent to your e-mail address.


The standard core mail functionality is used, and no hook or rule is used for that registration. 

Why doesn't the message appear?

I tried changing theme, but the message is still not appearing. Furthermore:


The $message variable is available in the template file
I am not using the Boost module; I am using the Mime Mail module to get HTML emails


How do i customize the message in some hooks?
A workaround would be to manually create message in hook_user_insert, with code like:

function mymodule_user_insert(&amp;$edit, $account, $category) {
  drupal_set_message(t('Account created, wait for approval.'), 'status');
}


Alternative place is hook_entity_insert:

function mymodule_entity_insert($entity, $type) {
  if ($type == 'user') {
    drupal_set_message(t('Account created, wait for approval.'), 'status');
  }
}


Problem is - it is possible that the same error will hide this one too. Benefit: it's easier to experiment with small custom hook, than to debug core.