class EntityChangedConstraintValidator

class EntityChangedConstraintValidator extends ConstraintValidator {
    
    /**
     * {@inheritdoc}
     */
    public function validate($entity, Constraint $constraint) {
        if (isset($entity)) {
            
            /** @var \Drupal\Core\Entity\EntityInterface $entity */
            if (!$entity->isNew()) {
                $saved_entity = \Drupal::entityTypeManager()->getStorage($entity->getEntityTypeId())
                    ->loadUnchanged($entity->id());
                // Ensure that all the entity translations are the same as or newer
                // than their current version in the storage in order to avoid
                // reverting other changes. In fact the entity object that is being
                // saved might contain an older entity translation when different
                // translations are being concurrently edited.
                if ($saved_entity) {
                    $common_translation_languages = array_intersect_key($entity->getTranslationLanguages(), $saved_entity->getTranslationLanguages());
                    foreach (array_keys($common_translation_languages) as $langcode) {
                        // Merely comparing the latest changed timestamps across all
                        // translations is not sufficient since other translations may have
                        // been edited and saved in the meanwhile. Therefore, compare the
                        // changed timestamps of each entity translation individually.
                        if ($saved_entity->getTranslation($langcode)
                            ->getChangedTime() > $entity->getTranslation($langcode)
                            ->getChangedTime()) {
                            $this->context
                                ->addViolation($constraint->message);
                            break;
                        }
                    }
                }
            }
        }
    }

}