Non-English item titles break nav ID generation

drupal_html_id function doesn't work with non-English strings and it breaks $id generation for tabs. You can wrap it with something like this to work:

$id = 'bootstrap-fieldgroup-nav-item--' . drupal_html_id(ctools_cleanstring($item['#title'], array('transliterate'=>TRUE)));

But I think this would be better:

$id = 'bootstrap-fieldgroup-nav-item--' . drupal_html_id($key);

You can test it with this title: "Описание"