diff --git a/core/lib/Drupal/Core/StringTranslation/StringTranslationTrait.php b/core/lib/Drupal/Core/StringTranslation/StringTranslationTrait.php
index c435f79..34877ec 100644
--- a/core/lib/Drupal/Core/StringTranslation/StringTranslationTrait.php
+++ b/core/lib/Drupal/Core/StringTranslation/StringTranslationTrait.php
@@ -100,11 +100,9 @@ protected function getNumberOfPlurals($langcode = NULL) {
    *   The string translation service.
    */
   protected function getStringTranslation() {
-    if (!$this->stringTranslation) {
-      $this->stringTranslation = \Drupal::service('string_translation');
-    }
-
-    return $this->stringTranslation;
+    // @todo Make this trait use DependencySerializationTrait to ensure that
+    // $this->stringTranslation can be serialized.
+    return $this->stringTranslation ?: \Drupal::service('string_translation');
   }
 
   /**
diff --git a/core/modules/locale/tests/src/Kernel/EntityTypeSerializationTest.php b/core/modules/locale/tests/src/Kernel/EntityTypeSerializationTest.php
new file mode 100644
index 0000000..66db456
--- /dev/null
+++ b/core/modules/locale/tests/src/Kernel/EntityTypeSerializationTest.php
@@ -0,0 +1,41 @@
+<?php
+
+namespace Drupal\Tests\locale\Kernel;
+
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests that entity type definitions can be serialized when Locale is present.
+ *
+ * @group locale
+ */
+class EntityTypeSerializationTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = [
+    'entity_test',
+    'field',
+    'file',
+    'language',
+    'locale',
+    'text',
+  ];
+
+  public function testEntityTypeSerializationWithTranslationService() {
+    /** @var \Drupal\Core\Entity\ContentEntityType $entity_type */
+    $entity_type = $this->container
+      ->get('entity_type.manager')
+      ->getDefinition('entity_test');
+
+    // Because the entity_test entity type does not explicitly define its plural
+    // label, this will result in a call to getStringTranslation(), which will
+    // implicitly cause $entity_type to reference the string_translation service
+    // and therefore become impossible to serialize due to the implicit
+    // dependency on the database connection (via locale's translator).
+    $entity_type->getPluralLabel();
+    serialize($entity_type);
+  }
+
+}