Render the field.
$values: The values retrieved from the database.
Overrides FieldPluginBase::render
function render($values) {
// @todo: Drupal Core dropped native language until config translation is
// ready, see http://drupal.org/node/1616594.
$value = $this
->get_value($values);
$language = language_load($value);
return $language ? $language->name : '';
}