diff --git a/core/modules/language/src/Tests/LanguageListTest.php b/core/modules/language/src/Tests/LanguageListTest.php
index 72e2b0a..5391a9f 100644
--- a/core/modules/language/src/Tests/LanguageListTest.php
+++ b/core/modules/language/src/Tests/LanguageListTest.php
@@ -154,6 +154,7 @@ function testLanguageList() {
       'direction' => Language::DIRECTION_LTR,
     );
     $this->drupalPostForm('admin/config/regional/language/add', $edit, t('Add custom language'));
+    $this->rebuildContainer();
     $this->assertUrl(\Drupal::url('entity.configurable_language.collection', [], ['absolute' => TRUE]));
     $this->assertText($name, 'Name found.');
 
diff --git a/core/modules/simpletest/src/Tests/SimpleTestWithLanguageTest.php b/core/modules/simpletest/src/Tests/SimpleTestWithLanguageTest.php
new file mode 100644
index 0000000..a0e379b
--- /dev/null
+++ b/core/modules/simpletest/src/Tests/SimpleTestWithLanguageTest.php
@@ -0,0 +1,63 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\simpletest\Tests\SimpleTestWithLanguageTest.
+ */
+
+namespace Drupal\simpletest\Tests;
+
+use Drupal\Component\Utility\Crypt;
+use Drupal\language\Tests\LanguageListTest;
+
+/**
+ * Tests SimpleTest's when language module is enabled.
+ *
+ * @group simpletest
+ */
+class SimpleTestWithLanguageTest extends LanguageListTest {
+
+  public static $modules = [
+    'simpletest',
+    'language',
+    'locale',
+  ];
+
+  /**
+   * Overrides DrupalWebTestCase::setUp().
+   */
+  protected function setUp() {
+    parent::setUp();
+    if (!$this->isInChildSite()) {
+      $this->drupalLogin($this->drupalCreateUser(array('administer unit tests')));
+    }
+  }
+
+  /**
+   * Ensures the tests run well with language module enabled.
+   */
+  public function testLanguageList() {
+    if ($this->isInChildSite()) {
+      // Ensure the .htkey file exists since this is only created just before a
+      // request. This allows the stub test to make requests. The event does not
+      // fire here and drupal_generate_test_ua() can not generate a key for a
+      // test in a test since the prefix has changed.
+      // @see \Drupal\Core\Test\HttpClientMiddleware\TestHttpClientMiddleware::onBeforeSendRequest()
+      // @see drupal_generate_test_ua();
+      $key_file = DRUPAL_ROOT . '/sites/simpletest/' . substr($this->databasePrefix, 10) . '/.htkey';
+      $private_key = Crypt::randomBytesBase64(55);
+      file_put_contents($key_file, $private_key);
+
+      // Only run following code if this test is running itself through a CURL
+      // request.
+      parent::testLanguageList();
+    }
+    else {
+      $edit['tests[Drupal\simpletest\Tests\SimpleTestWithLanguageTest]'] = TRUE;
+      $this->drupalPostForm('admin/config/development/testing', $edit, t('Run tests'));
+      $this->assertRaw('0 exceptions');
+      $this->assertRaw('0 fails');
+    }
+  }
+
+}