unset description in user_profile_form

Hi

I try to remove descriptions of language, files (avatar) and timezone in user profile form:

function bartik_form_alter(&$form, $form_state, $form_id) {

if ($form_id == 'user_profile_form') {
                unset($form['account']['mail']['#description']);
		unset($form['account']['pass']['#description']);
		unset($form['account']['language']['#description']);
		unset($form['account']['files']['#description']);
		unset($form['account']['timezone']['#description']);
   }
}

This code removes mail and password descriptions but it does not removes language, files and timezone descriptions.

Please, what is wrong with this code?

Thank you

Drupal version: 


Source: https://www.drupal.org/taxonomy/term/22/feed