How to change the 'Name' label on term add/edit pages programmatically?
If you mean you want to change the title of the form element, then it is basically the same as it was in 7.x.

/**
 * Implements hook_form_alter().
 */
function MYMODULE_form_alter(&amp;$form, FormStateInterface $form_state, $form_id) {
  if ($form_id == 'taxonomy_MYVOCABULARY_form') {
    $form['foo']['#title'] = t('New Title');
  }
}


Adding in what 4k4 said... field widgets behave differently than general form items:

$form['name']['widget'][0]['value']['#title'] = 'New Title';