diff -u b/core/modules/taxonomy/taxonomy.install b/core/modules/taxonomy/taxonomy.install
--- b/core/modules/taxonomy/taxonomy.install
+++ b/core/modules/taxonomy/taxonomy.install
@@ -202,7 +202,25 @@
 function taxonomy_update_8702() {
-  $database = \Drupal::database();
-  $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->getId();
-  $database->update('taxonomy_term__parent')
-    ->fields(['langcode' => $default_langcode])
-    ->execute();
+  $definition_update_manager = \Drupal::entityDefinitionUpdateManager();
+  /** @var \Drupal\Core\Field\BaseFieldDefinition $field_storage_definition */
+  $field_storage_definition = $definition_update_manager->getFieldStorageDefinition('parent', 'taxonomy_term');
+
+  // Only perform the update if the field is not translatable. It's possible
+  // that custom or contrib code has overridden this.
+  if (!$field_storage_definition->isTranslatable()) {
+    $default_langcode = \Drupal::languageManager()
+      ->getDefaultLanguage()
+      ->getId();
+    // taxonomy_update_8502() populated the langcode field of
+    // 'taxonomy_term__parent' using the term's langcode but the field is not
+    // translatable. If taxonomy_post_update_make_taxonomy_term_revisionable()
+    // has already run prior to
+    // https://www.drupal.org/project/drupal/issues/3066439 then this will have
+    // already fixed the field. However on sites that have not run that update
+    // yet we need to run this update the langcode as calling
+    // \Drupal\Core\Entity\Sql\SqlContentEntityStorage::restore() no longer
+    // calls \Drupal\taxonomy\Entity\Term::preSave().
+    \Drupal::database()->update('taxonomy_term__parent')
+      ->fields(['langcode' => $default_langcode])
+      ->execute();
+  }
 }