Implements hook_FORM_ID_alter().
function tmgmt_content_form_field_config_edit_form_alter(&$form, FormStateInterface $form_state) {
/** @var \Drupal\field\Entity\FieldConfig $field_config */
$field_config = $form_state
->getFormObject()
->getEntity();
$bundle_is_translatable = \Drupal::service('content_translation.manager')
->isEnabled($field_config
->getTargetEntityTypeId(), $field_config
->getTargetBundle());
$form['tmgmt_content_excluded'] = array(
'#type' => 'checkbox',
'#title' => t('Exclude from translations'),
'#weight' => 0,
'#default_value' => $field_config
->getThirdPartySetting('tmgmt_content', 'excluded', 0),
'#description' => t('This field will no longer be exported and translated by Translation Management Tool but can still be translated manually.'),
'#states' => [
'visible' => [
':input[name="translatable"]' => [
'checked' => TRUE,
],
],
],
'#access' => $bundle_is_translatable,
);
$form['#entity_builders'][] = 'tmgmt_content_entity_builder';
}