Can I get the Node's content type in hook_flag_alter
If you're using flag 2.x with Drupal 7, then this should give you what you want.

function hook_flag_alter(&amp;$flag) {
    $type_text = "";
    switch($flag-&gt;entity_type) {
      case 'node':
        switch(reset($flag-&gt;types)) {
          case 'page':
            $type_text = t('Page');
            break;
          case 'blog':
            $type_text = t('Blog Post');
            break;
          default:
            $type_text = t('Node');
        }
        break;
      case 'user':
        $type_text = ('User');
        break;
      default:
    }

    $flag-&gt;flag_short = t('Follow @type', array('@type' =&gt; $type_text));
    $flag-&gt;unflag_short = t('Unfollow @type', array('@type' =&gt; $type_text));
}


Note: This code assumes that each flag only applies for a single content type.