Perform alterations on field_attach_prepare_translation().
This hook is invoked after the field module has performed the operation.
\Drupal\Core\Entity\EntityInterface $entity: The entity being prepared for translation.
$context: An associative array containing:
function hook_field_attach_prepare_translation_alter(\Drupal\Core\Entity\EntityInterface $entity, $context) {
if ($entity
->entityType() == 'custom_entity_type') {
$entity->custom_field = $context['source_entity']->custom_field;
}
}