reverted:
--- b/core/modules/simpletest/src/TestBase.php
+++ a/core/modules/simpletest/src/TestBase.php
@@ -11,7 +11,6 @@
 use Drupal\Component\Utility\Random;
 use Drupal\Core\Database\Database;
 use Drupal\Component\Utility\String;
-use Drupal\Core\DrupalKernel;
 use Drupal\Core\Config\ConfigImporter;
 use Drupal\Core\Config\StorageComparer;
 use Drupal\Core\DependencyInjection\ContainerBuilder;
@@ -1120,9 +1119,7 @@
     }
 
     // Backup current in-memory configuration.
+    $this->originalSite = conf_path();
-    $request = Request::createFromGlobals();
-    $conf_path = DrupalKernel::findSitePath($request);
-    $this->originalSite = $conf_path;
     $this->originalSettings = Settings::getAll();
     $this->originalConfig = $GLOBALS['config'];
     // @todo Remove all remnants of $GLOBALS['conf'].
@@ -1137,7 +1134,7 @@
     // Save further contextual information.
     // Use the original files directory to avoid nesting it within an existing
     // simpletest directory if a test is executed within a test.
+    $this->originalFileDirectory = Settings::get('file_public_path', conf_path() . '/files');
-    $this->originalFileDirectory = Settings::get('file_public_path', $conf_path . '/files');
     $this->originalProfile = drupal_get_profile();
     $this->originalUser = isset($user) ? clone $user : NULL;
 
@@ -1207,7 +1204,7 @@
     // After preparing the environment and changing the database prefix, we are
     // in a valid test environment.
     drupal_valid_test_ua($this->databasePrefix);
+    conf_path(FALSE, TRUE);
-    DrupalKernel::findSitePath($request);
 
     // Reset settings.
     new Settings(array(
@@ -1321,7 +1318,7 @@
     else {
       drupal_valid_test_ua(FALSE);
     }
+    conf_path(TRUE, TRUE);
-    DrupalKernel::findSitePath($request);
 
     // Restore original shutdown callbacks.
     $callbacks = &drupal_register_shutdown_function();
only in patch2:
unchanged:
--- a/core/modules/locale/locale.install
+++ b/core/modules/locale/locale.install
@@ -5,9 +5,11 @@
  * Install, update, and uninstall functions for the Locale module.
  */
 
+use Drupal\Core\DrupalKernel;
 use Drupal\Core\Url;
 use Drupal\Core\Language\Language;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationSelected;
+use Symfony\Component\HttpFoundation\Request;
 
 /**
  * Implements hook_install().
@@ -15,7 +17,9 @@
 function locale_install() {
   // Create the interface translations directory and ensure it's writable.
   if (!$directory = \Drupal::config('locale.settings')->get('translation.path')) {
-    $directory = conf_path() . '/files/translations';
+    $request = Request::createFromGlobals();
+    $conf_path = DrupalKernel::findSitePath($request);
+    $directory = $conf_path . '/files/translations';
     \Drupal::configFactory()->getEditable('locale.settings')->set('translation.path', $directory)->save();
   }
   file_prepare_directory($directory, FILE_CREATE_DIRECTORY | FILE_MODIFY_PERMISSIONS);