--- /dev/null
+<?php
+
+namespace Drupal\entity_test\Entity;
+
+/**
+ * Defines a test entity class using a custom langcode entity key.
+ *
+ * @ContentEntityType(
+ * id = "entity_test_mul_langcode_key",
+ * label = @Translation("Test entity - data table - langcode key"),
+ * handlers = {
+ * "view_builder" = "Drupal\entity_test\EntityTestViewBuilder",
+ * "access" = "Drupal\entity_test\EntityTestAccessControlHandler",
+ * "form" = {
+ * "default" = "Drupal\entity_test\EntityTestForm",
+ * "delete" = "Drupal\entity_test\EntityTestDeleteForm"
+ * },
+ * "translation" = "Drupal\content_translation\ContentTranslationHandler",
+ * "views_data" = "Drupal\views\EntityViewsData",
+ * "route_provider" = {
+ * "html" = "Drupal\Core\Entity\Routing\DefaultHtmlRouteProvider",
+ * },
+ * },
+ * base_table = "entity_test_mul_langcode_key",
+ * data_table = "entity_test_mul_langcode_key_field_data",
+ * admin_permission = "administer entity_test content",
+ * translatable = TRUE,
+ * entity_keys = {
+ * "id" = "id",
+ * "uuid" = "uuid",
+ * "bundle" = "type",
+ * "label" = "name",
+ * "langcode" = "custom_langcode_key",
+ * "default_langcode" = "custom_default_langcode_key",
+ * },
+ * links = {
+ * "add-form" = "/entity_test_mul_langcode_key/add",
+ * "canonical" = "/entity_test_mul_langcode_key/manage/{entity_test_mul_langcode_key}",
+ * "edit-form" = "/entity_test_mul_langcode_key/manage/{entity_test_mul_langcode_key}/edit",
+ * "delete-form" = "/entity_test/delete/entity_test_mul_langcode_key/{entity_test_mul_langcode_key}",
+ * },
+ * field_ui_base_route = "entity.entity_test_mul_langcode_key.admin_form",
+ * )
+ */
+class EntityTestMulLangcodeKey extends EntityTest {
+
+}