diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
index 68adee1..4b7057a 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
@@ -83,9 +83,14 @@
   /**
    * The language code of the entity's default language.
    *
+   * Assumed to be English by default. ConfigEntityStorage will set an
+   * appropriate language when creating new entities. This default applies to
+   * imported default configuration where the language code is missing. Those
+   * should be assumed to be English.
+   *
    * @var string
    */
-  protected $langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED;
+  protected $langcode = 'en';
 
   /**
    * Third party entity settings.
diff --git a/core/modules/rdf/src/Entity/RdfMapping.php b/core/modules/rdf/src/Entity/RdfMapping.php
index 577cbe7..3e97d63 100644
--- a/core/modules/rdf/src/Entity/RdfMapping.php
+++ b/core/modules/rdf/src/Entity/RdfMapping.php
@@ -9,6 +9,7 @@
 
 use Drupal\Core\Config\Entity\ConfigEntityBase;
 use Drupal\Core\Entity\EntityStorageInterface;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\rdf\RdfMappingInterface;
 
 /**
@@ -26,6 +27,15 @@
 class RdfMapping extends ConfigEntityBase implements RdfMappingInterface {
 
   /**
+   * The language code of the entity's default language.
+   *
+   * This entity type does not have translatable elements.
+   *
+   * @var string
+   */
+  protected $langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED;
+
+  /**
    * Unique ID for the config entity.
    *
    * @var string