EntityUntranslatableFieldsConstraint.php

<?php

namespace Drupal\Core\Entity\Plugin\Validation\Constraint;

use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\Core\Validation\Attribute\Constraint;
use Symfony\Component\Validator\Constraint as SymfonyConstraint;

/**
 * Validation constraint for the entity changed timestamp.
 */
class EntityUntranslatableFieldsConstraint extends SymfonyConstraint {
    public $defaultRevisionMessage = 'Non-translatable fields can only be changed when updating the current revision.';
    public $defaultTranslationMessage = 'Non-translatable fields can only be changed when updating the original language.';

}