class EntityReferenceTranslationDeriver

class EntityReferenceTranslationDeriver extends DeriverBase implements ContainerDeriverInterface {
  use StringTranslationTrait;

  /**
   * The entity field manager.
   *
   * @var \Drupal\Core\Entity\EntityFieldManagerInterface
   */
  protected $entityFieldManager;

  /**
   * The entity type manager.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;

  /**
   * EntityReferenceTranslationDeriver constructor.
   *
   * @param string $base_plugin_id
   *   The base plugin ID.
   * @param \Drupal\Core\Entity\EntityFieldManagerInterface $entity_field_manager
   *   The entity field manager.
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager.
   */
  public function __construct($base_plugin_id, EntityFieldManagerInterface $entity_field_manager, EntityTypeManagerInterface $entity_type_manager) {
    $this->entityFieldManager = $entity_field_manager;
    $this->entityTypeManager = $entity_type_manager;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, $base_plugin_id) {
    return new static($base_plugin_id, $container
      ->get('entity_field.manager'), $container
      ->get('entity_type.manager'));
  }

  /**
   * {@inheritdoc}
   */
  public function getDerivativeDefinitions($base_plugin_definition) {

    // Get all entity reference fields.
    $field_map = $this->entityFieldManager
      ->getFieldMapByFieldType('entity_reference');
    foreach ($field_map as $entity_type => $fields) {
      foreach ($fields as $field_name => $field) {
        foreach ($field['bundles'] as $bundle) {
          $field_definitions = $this->entityFieldManager
            ->getFieldDefinitions($entity_type, $bundle);
          $target_type = $field_definitions[$field_name]
            ->getSetting('target_type');

          // If the field's target type is not supported, skip it.
          if (!array_key_exists($target_type, $base_plugin_definition['target_types'])) {
            continue;
          }

          // Key derivatives by entity types and bundles.
          $derivative_key = $entity_type . '__' . $bundle;
          $derivative = $base_plugin_definition;
          $entity_type_definition = $this->entityTypeManager
            ->getDefinition($entity_type);

          // Set the migration label.
          $derivative['label'] = $this
            ->t('@label (@derivative)', [
            '@label' => $base_plugin_definition['label'],
            '@derivative' => $derivative_key,
          ]);

          // Set the source plugin.
          $derivative['source']['plugin'] = 'content_entity' . PluginBase::DERIVATIVE_SEPARATOR . $entity_type;
          if ($entity_type_definition
            ->hasKey('bundle')) {
            $derivative['source']['bundle'] = $bundle;
          }

          // Set the process pipeline.
          $id_key = $entity_type_definition
            ->getKey('id');
          $derivative['process'][$id_key] = $id_key;
          if ($entity_type_definition
            ->isRevisionable()) {
            $revision_key = $entity_type_definition
              ->getKey('revision');
            $derivative['process'][$revision_key] = $revision_key;
          }
          if ($entity_type_definition
            ->isTranslatable()) {
            $langcode_key = $entity_type_definition
              ->getKey('langcode');
            $derivative['process'][$langcode_key] = $langcode_key;
          }

          // Set the destination plugin.
          $derivative['destination']['plugin'] = 'entity' . PluginBase::DERIVATIVE_SEPARATOR . $entity_type;
          if ($entity_type_definition
            ->hasKey('bundle')) {
            $derivative['destination']['default_bundle'] = $bundle;
          }
          if ($entity_type_definition
            ->isTranslatable()) {
            $derivative['destination']['translations'] = TRUE;
          }

          // Allow overwriting the entity reference field so we can update its
          // values with the ones found in the mapping table.
          $derivative['destination']['overwrite_properties'][$field_name] = $field_name;

          // Add the entity reference field to the process pipeline.
          $derivative['process'][$field_name] = [
            'plugin' => 'sub_process',
            'source' => $field_name,
            'process' => [
              'translation_target_id' => [
                [
                  'plugin' => 'migration_lookup',
                  'source' => 'target_id',
                  'migration' => $base_plugin_definition['target_types'][$target_type],
                  'no_stub' => TRUE,
                ],
                [
                  'plugin' => 'skip_on_empty',
                  'method' => 'process',
                ],
                [
                  'plugin' => 'extract',
                  'index' => [
                    0,
                  ],
                ],
              ],
              'target_id' => [
                [
                  'plugin' => 'null_coalesce',
                  'source' => [
                    '@translation_target_id',
                    'target_id',
                  ],
                ],
              ],
            ],
          ];
          if (!isset($this->derivatives[$derivative_key])) {

            // If this is a new derivative, add it to the returned derivatives.
            $this->derivatives[$derivative_key] = $derivative;
          }
          else {

            // If this is an existing derivative, it means this bundle has more
            // than one entity reference field. In that case, we only want to
            // add the field to the process pipeline and add it to
            // overwrite_properties so it can be overwritten.
            $this->derivatives[$derivative_key]['process'] += $derivative['process'];
            $this->derivatives[$derivative_key]['destination']['overwrite_properties'] += $derivative['destination']['overwrite_properties'];
          }
        }
      }
    }
    return $this->derivatives;
  }

}