diff -u b/core/lib/Drupal/Core/Config/DatabaseStorage.php b/core/lib/Drupal/Core/Config/DatabaseStorage.php
--- b/core/lib/Drupal/Core/Config/DatabaseStorage.php
+++ b/core/lib/Drupal/Core/Config/DatabaseStorage.php
@@ -77,8 +77,8 @@
     if (isset($data[$name])) {
       return $data[$name];
     }
-    // @todo change to return to be consistent with other parts of Drupal, for
-    //   example, loading an entity returns NULL if it does not exist.
+    // @todo https://drupal.org/node/2260961 change return NULL when no
+    //   configuration object found to be consistent with other parts of Drupal.
     return FALSE;
   }
 
diff -u b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverride.php b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverride.php
--- b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverride.php
+++ b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverride.php
@@ -8,7 +8,9 @@
 namespace Drupal\language\Config;
 
 use Drupal\Core\Config\Config;
+use Drupal\Core\Config\ConfigImporter;
 use Drupal\Core\Config\FileStorage;
+use Drupal\Core\Config\StorageComparer;
 use Drupal\Core\Config\StorageInterface;
 use Drupal\Core\Config\TypedConfigManagerInterface;
 use Drupal\Core\Language\Language;
@@ -177,2 +179,108 @@
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getStorages() {
+    $storages = array();
+    foreach (\Drupal::languageManager()->getLanguages() as $language) {
+      $storages[] = $this->getStorage($language->getId());
+    }
+    return $storages;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function configSyncStep(&$context, ConfigImporter $config_importer) {
+    // First time get create list of stuff to import.
+    if (!isset($context['sandbox']['language'])) {
+      static::initializeSandbox($context, $config_importer);
+    }
+
+    if ($to_process = static::getNextOperation($context)) {
+      list($config_name, $langcode, $op, $comparer) = $to_process;
+
+      if ($op == 'delete') {
+        $comparer->getTargetStorage()->delete($config_name);
+      }
+      else {
+        $comparer->getTargetStorage()->write($config_name, $comparer->getSourceStorage()->read($config_name));
+      }
+      $context['sandbox']['language']['data'][$langcode]['processed'][$op][] = $config_name;
+      $context['sandbox']['language']['processed']++;
+      $context['finished'] = $context['sandbox']['language']['processed'] / $context['sandbox']['language']['total_to_process'];
+      $context['message'] = \Drupal::translation()->translate('Processing @name language configuration override for langcode @langcode.', array('@name' => $config_name, '@langcode' => $langcode));
+    }
+    else {
+      $context['finished'] = 1;
+    }
+
+  }
+
+  /**
+   * Initializes the batch context with what to do.
+   *
+   * @param array $context
+   *   The batch context.
+   * @param \Drupal\Core\Config\ConfigImporter $config_importer
+   *   The config importer.
+   */
+  protected static function initializeSandbox(&$context, $config_importer) {
+    $context['sandbox']['language']['total_to_process'] = 0;
+    $context['sandbox']['language']['processed'] = 0;
+    $context['sandbox']['language']['current_langcode'] = NULL;
+    $context['sandbox']['language']['data'] = array();
+    // All languages are synced by now.
+    foreach (\Drupal::languageManager()->getLanguages() as $language) {
+      // Get the active store for the language
+      $active = \Drupal::languageManager()->getLanguageConfigOverrideStorage($language->getId());
+      // So we are tying ourselves into files unlike the current ConfigSync
+      // which is just using config.storage.staging. If we don't want to do this
+      // we are going to have to expand the staging storage functionality to
+      // deal with overrides. Which might be a good idea anyway.
+      $stage = new FileStorage(config_get_config_directory(CONFIG_STAGING_DIRECTORY) . '/language/' . $language->getId());
+      $comparer = new StorageComparer($stage, $active);
+      $comparer->createChangelist();
+      $count = 0;
+      foreach (array('delete', 'create', 'rename', 'update') as $op) {
+        $count += count($comparer->getChangelist($op));
+      }
+      if ($count > 0) {
+        $context['sandbox']['language']['data'][$language->getId()]['comparer'] = $comparer;
+        $context['sandbox']['language']['data'][$language->getId()]['processed'] = $comparer->getEmptyChangelist();
+        $context['sandbox']['language']['data'][$language->getId()]['finished'] = FALSE;
+        $context['sandbox']['language']['total_to_process'] += $count;
+      }
+    }
+  }
+
+  /**
+   * Gets the language code to process.
+   *
+   * @param $context
+   *   The batch context.
+   *
+   * @return array
+   *   An array containing data need to process the next config override.
+   */
+  protected static function getNextOperation(&$context) {
+    foreach ($context['sandbox']['language']['data'] as $langcode => $data) {
+      if (!$data['finished']) {
+        $comparer = $context['sandbox']['language']['data'][$langcode]['comparer'];
+        foreach (array('delete', 'create', 'update') as $op) {
+          $todo = array_diff($comparer->getChangelist($op), $context['sandbox']['language']['data'][$langcode]['processed'][$op]);
+          if (!empty($todo)) {
+            $return[] = array_shift($todo);
+            $return[] = $langcode;
+            $return[] = $op;
+            $return[] = $comparer;
+            return $return;
+          }
+        }
+        $context['sandbox']['language']['data'][$langcode]['finished'] = TRUE;
+      }
+    }
+    return FALSE;
+  }
+
 }
diff -u b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverrideInterface.php b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverrideInterface.php
--- b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverrideInterface.php
+++ b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverrideInterface.php
@@ -8,13 +8,14 @@
 namespace Drupal\language\Config;
 
 use Drupal\Core\Config\ConfigFactoryOverrideInterface;
+use Drupal\Core\Config\ConfigFactoryOverrideSyncInterface;
 use Drupal\Core\Language\Language;
 use Drupal\Core\Language\LanguageDefault;
 
 /**
  * Defines the interface for a configuration factory language override object.
  */
-interface LanguageConfigFactoryOverrideInterface extends ConfigFactoryOverrideInterface {
+interface LanguageConfigFactoryOverrideInterface extends ConfigFactoryOverrideInterface, ConfigFactoryOverrideSyncInterface {
 
   /**
    * Prefix for all language configuration files.
diff -u b/core/modules/language/lib/Drupal/language/Config/LanguageOverrideDatabaseStorage.php b/core/modules/language/lib/Drupal/language/Config/LanguageOverrideDatabaseStorage.php
--- b/core/modules/language/lib/Drupal/language/Config/LanguageOverrideDatabaseStorage.php
+++ b/core/modules/language/lib/Drupal/language/Config/LanguageOverrideDatabaseStorage.php
@@ -165,12 +165,11 @@
    * {@inheritdoc}
    */
   public function setLangcode($langcode) {
-    // Prevent side effects from switching changing a storage's langcode. The
-    // configuration override objects returned from
+    // Mitigate side effects by preventing the storage's langcode changing once
+    // set. The configuration override objects returned from
     // \Drupal\language\Config\LanguageConfigFactoryOverride::getOverride()
     // have a storage object injected so allowing the langcode to be changed
-    // once set could create a mismatch between the language of the data and the
-    // storage.
+    // could create a mismatch between the language of the data and the storage.
     if (isset($this->langcode) && $langcode !== $this->langcode) {
       throw new LanguageOverrideStorageLockedException('Cannot switch language override storage langcode once it has been set.');
     }
@@ -180,2 +179,9 @@
 
+  public function getExportDir() {
+    if (!isset($this->langcode)) {
+      throw new \Exception('Wha?');
+    }
+    return 'language/' . $this->langcode;
+  }
+
 }
diff -u b/core/modules/language/lib/Drupal/language/Config/LanguageOverrideStorageInterface.php b/core/modules/language/lib/Drupal/language/Config/LanguageOverrideStorageInterface.php
--- b/core/modules/language/lib/Drupal/language/Config/LanguageOverrideStorageInterface.php
+++ b/core/modules/language/lib/Drupal/language/Config/LanguageOverrideStorageInterface.php
@@ -14,7 +14,9 @@
   /**
    * Sets the langcode to determine the override configuration directory to use.
    *
-   * Implementations
+   * Implementations should prevent the langcode from changing once set and
+   * throw a \Drupal\language\Exception\LanguageOverrideStorageLockedException
+   * if this occurs.
    *
    * @param string $langcode
    *   The language langcode to get the directory for.
only in patch2:
unchanged:
--- /dev/null
+++ b/core/lib/Drupal/Core/Config/ConfigFactoryOverrideSyncInterface.php
@@ -0,0 +1,31 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Config\ConfigFactoryOverrideSyncInterface.
+ */
+
+namespace Drupal\Core\Config;
+
+/**
+ * Defines the interface for a configuration factory override objects that
+ * interface with export and synchronisation of config.
+ */
+interface ConfigFactoryOverrideSyncInterface {
+
+  /**
+   * @return \Drupal\Core\Config\StorageInterface[]
+   */
+  public function getStorages();
+
+  /**
+   * Processes staged override data as part of a configuration sync.
+   *
+   * @param array $context
+   *   The batch context.
+   * @param \Drupal\Core\Config\ConfigImporter $config_importer
+   *   The config importer.
+   */
+  public static function configSyncStep(&$context, ConfigImporter $config_importer);
+
+}
only in patch2:
unchanged:
--- a/core/lib/Drupal/Core/Config/ConfigImporter.php
+++ b/core/lib/Drupal/Core/Config/ConfigImporter.php
@@ -542,6 +542,8 @@ public function initialize() {
       $sync_steps[] = 'processExtensions';
     }
     $sync_steps[] = 'processConfigurations';
+    // Allow any overrides to hook into the import. Since overr
+    $sync_steps[] = 'processOverrides';
 
     // Allow modules to add new steps to configuration synchronization.
     $this->moduleHandler->alter('config_import_steps', $sync_steps, $this);
@@ -602,6 +604,38 @@ public function processConfigurations(array &$context) {
     }
   }
 
+  public function processOverrides(array &$context) {
+     if (!isset($context['sandbox']['overrides'])) {
+      // Allow overriders to process staged configuration.
+      $context['sandbox']['overrides'] = array();
+      $context['sandbox']['override_count'] = 0;
+      $context['sandbox']['override_progress_count'] = 0;
+      foreach ($this->configManager->getConfigFactory()->getOverrides() as $overrider) {
+        if ($overrider instanceof ConfigFactoryOverrideSyncInterface) {
+          $context['sandbox']['overrides'][] = array(get_class($overrider), 'configSyncStep');
+          $context['sandbox']['override_count']++;
+        }
+      }
+    }
+    if (empty($context['sandbox']['overrides'])) {
+      $context['finished'] = 1;
+    }
+    else {
+      $callable = current($context['sandbox']['overrides']);
+      call_user_func_array($callable, array(&$context, $this));
+      // Have to change $context['finished'] to account for the fact there maybe
+      // more that one overrider.
+      $new_finished = ($context['sandbox']['override_progress_count'] + $context['finished']) / $context['sandbox']['override_count'];
+      if ($context['finished'] == 1) {
+        // We've complete the current process - remove it.
+        array_shift($context['sandbox']['overrides']);
+
+        $context['sandbox']['override_progress_count']++;
+      }
+      $context['finished'] = $new_finished;
+    }
+  }
+
   /**
    * Finishes the batch.
    *
@@ -997,7 +1031,7 @@ public function getId() {
    */
   protected function reInjectMe() {
     $this->eventDispatcher = \Drupal::service('event_dispatcher');
-    $this->configFactory = \Drupal::configFactory();
+    $this->configManager = \Drupal::service('config.manager');
     $this->entityManager = \Drupal::entityManager();
     $this->lock = \Drupal::lock();
     $this->typedConfigManager = \Drupal::service('config.typed');
only in patch2:
unchanged:
--- a/core/modules/config/lib/Drupal/config/Controller/ConfigController.php
+++ b/core/modules/config/lib/Drupal/config/Controller/ConfigController.php
@@ -9,6 +9,7 @@
 
 use Drupal\Core\Archiver\ArchiveTar;
 use Drupal\Component\Serialization\Yaml;
+use Drupal\Core\Config\ConfigFactoryOverrideSyncInterface;
 use Drupal\Core\Config\ConfigManagerInterface;
 use Drupal\Core\Config\StorageInterface;
 use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
@@ -89,6 +90,19 @@ public function downloadExport() {
       $archiver->addString("$name.yml", Yaml::encode(\Drupal::config($name)->get()));
     }
 
+    // Allow overriders to add files to the export.
+    foreach (\Drupal::configFactory()->getOverrides() as $overrider) {
+      if ($overrider instanceof ConfigFactoryOverrideSyncInterface) {
+        foreach ($overrider->getStorages() as $storage) {
+          // @todo consider adding getExportDir to interface. But where?
+          $overrider_dir = $storage->getExportDir();
+          foreach ($storage->listAll() as $name) {
+            $archiver->addString($overrider_dir . '/' . $name . '.yml', Yaml::encode($storage->read($name)));
+          }
+        }
+      }
+    }
+
     $request = new Request(array('file' => 'config.tar.gz'));
     return $this->fileDownloadController->download($request, 'temporary');
   }
only in patch2:
unchanged:
--- a/core/modules/config/lib/Drupal/config/Form/ConfigSync.php
+++ b/core/modules/config/lib/Drupal/config/Form/ConfigSync.php
@@ -8,6 +8,7 @@
 namespace Drupal\config\Form;
 
 use Drupal\Component\Uuid\UuidInterface;
+use Drupal\Core\Config\ConfigFactoryOverrideSyncInterface;
 use Drupal\Core\Config\ConfigImporterException;
 use Drupal\Core\Config\ConfigImporter;
 use Drupal\Core\Entity\EntityManagerInterface;
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageConfigOverrideImportTest.php
@@ -0,0 +1,71 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\language\Tests\LanguageConfigOverrideImportTest.
+ */
+
+namespace Drupal\language\Tests;
+
+use Drupal\Core\Config\FileStorage;
+use Drupal\Core\Language\Language;
+use Drupal\simpletest\WebTestBase;
+
+class LanguageConfigOverrideImportTest extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = array('language', 'config', 'config_translation');
+
+  public static function getInfo() {
+    return array(
+      'name' => 'Language config override synchronize',
+      'description' => 'Ensures the language config overrides can be synchronized.',
+      'group' => 'Language',
+    );
+  }
+
+  public function setUp() {
+    parent::setUp();
+    $this->adminUser = $this->drupalCreateUser(array('translate configuration'));
+    $this->drupalLogin($this->adminUser);
+  }
+
+  /**
+   *
+   */
+  public function testConfigOverrideImport() {
+    language_save(new Language(array(
+      'name' => 'French',
+      'id' => 'fr',
+    )));
+    /* @var \Drupal\Core\Config\StorageInterface $staging */
+    $staging = \Drupal::service('config.storage.staging');
+    $this->copyConfig(\Drupal::service('config.storage'), $staging);
+
+    \Drupal::moduleHandler()->uninstall(array('language'));
+    // Ensure that the current site has no overrides registered to the
+    // ConfigFactory.
+    $this->rebuildContainer();
+
+    /* @var \Drupal\Core\Config\StorageInterface $override_staging */
+    $override_staging = new FileStorage(config_get_config_directory(CONFIG_STAGING_DIRECTORY) . '/language/fr');
+    // Create some overrides in staging.
+    $override_staging->write('system.site', array('name' => 'FR default site name'));
+    $override_staging->write('system.maintenance', array('message' => 'FR message: @site is currently under maintenance. We should be back shortly. Thank you for your patience'));
+
+    $this->configImporter()->import();
+    $this->rebuildContainer();
+
+    $override = \Drupal::languageManager()->getLanguageConfigOverride('fr', 'system.site');
+    $this->assertEqual('FR default site name', $override->get('name'));
+    $this->drupalGet('fr');
+    $this->assertText('FR default site name');
+
+    $this->drupalGet('admin/config/development/maintenance/translate/fr/edit');
+    $this->assertText('FR message: @site is currently under maintenance. We should be back shortly. Thank you for your patience');
+  }
+}