diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
index 68adee1..90837f9 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
@@ -83,9 +83,18 @@
   /**
    * 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. All configuration entities support third
+   * party settings, so even configuration entities that do not directly
+   * store settings involving text in a human language may have such third
+   * party settings attached. This means configuration entities should be in one
+   * of the configured languages or the built-in English.
+   *
    * @var string
    */
-  protected $langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED;
+  protected $langcode = 'en';
 
   /**
    * Third party entity settings.
diff --git a/core/modules/field/tests/src/Unit/FieldConfigEntityUnitTest.php b/core/modules/field/tests/src/Unit/FieldConfigEntityUnitTest.php
index 992f698..6904110 100644
--- a/core/modules/field/tests/src/Unit/FieldConfigEntityUnitTest.php
+++ b/core/modules/field/tests/src/Unit/FieldConfigEntityUnitTest.php
@@ -243,7 +243,7 @@ public function testToArray() {
       'id' => 'test_entity_type.test_bundle.field_test',
       'uuid' => NULL,
       'status' => TRUE,
-      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
+      'langcode' => 'en',
       'field_name' => 'field_test',
       'entity_type' => 'test_entity_type',
       'bundle' => 'test_bundle',