diff --git a/core/modules/config_translation/src/Access/ConfigTranslationOverviewAccess.php b/core/modules/config_translation/src/Access/ConfigTranslationOverviewAccess.php
index 9537aad..51f6463 100644
--- a/core/modules/config_translation/src/Access/ConfigTranslationOverviewAccess.php
+++ b/core/modules/config_translation/src/Access/ConfigTranslationOverviewAccess.php
@@ -70,7 +70,18 @@ public function access(RouteMatchInterface $route_match, AccountInterface $accou
     /** @var \Drupal\config_translation\ConfigMapperInterface $mapper */
     $mapper = $this->configMapperManager->createInstance($route->getDefault('plugin_id'));
     $mapper->populateFromRouteMatch($route_match);
-    $this->sourceLanguage = $this->languageManager->getLanguage($mapper->getLangcode());
+
+    try {
+      $langcode = $mapper->getLangcode();
+    }
+    catch (\RuntimeException $exception) {
+      // ConfigTranslationController and ConfigTranslationFormBase show a
+      // helpful message if the language codes do not match, so do not let that
+      // prevent granting access.
+      $langcode = 'en';
+    }
+
+    $this->sourceLanguage = $this->languageManager->getLanguage($langcode);
 
     // Allow access to the translation overview if the proper permission is
     // granted, the configuration has translatable pieces, and the source
diff --git a/core/modules/config_translation/src/ConfigNamesMapper.php b/core/modules/config_translation/src/ConfigNamesMapper.php
index 5d15dd5..8efeb16 100644
--- a/core/modules/config_translation/src/ConfigNamesMapper.php
+++ b/core/modules/config_translation/src/ConfigNamesMapper.php
@@ -385,14 +385,7 @@ public function getTypeLabel() {
    * {@inheritdoc}
    */
   public function getLangcode() {
-    $config_factory = $this->configFactory;
-    $langcodes = array_map(function($name) use ($config_factory) {
-      // Default to English if no language code was provided in the file.
-      // Although it is a best practice to include a language code, if the
-      // developer did not think about a multilingual use-case, we fall back
-      // on assuming the file is English.
-      return $config_factory->get($name)->get('langcode') ?: 'en';
-    }, $this->getConfigNames());
+    $langcodes = array_map([$this, 'getLangcodeFromConfig'], $this->getConfigNames());
 
     if (count(array_unique($langcodes)) > 1) {
       throw new \RuntimeException('A config mapper can only contain configuration for a single language.');
@@ -402,6 +395,23 @@ public function getLangcode() {
   }
 
   /**
+   * Returns the language code of a configuration object given its name.
+   *
+   * @param string $config_name
+   *   The name of the configuration object.
+   *
+   * @return string
+   *   The language code of the configuration object.
+   */
+  public function getLangcodeFromConfig($config_name) {
+    // Default to English if no language code was provided in the file.
+    // Although it is a best practice to include a language code, if the
+    // developer did not think about a multilingual use-case, we fall back
+    // on assuming the file is English.
+    return $this->configFactory->get($config_name)->get('langcode') ?: 'en';
+  }
+
+  /**
    * {@inheritdoc}
    */
   public function setLangcode($langcode) {
diff --git a/core/modules/config_translation/src/Form/ConfigTranslationFormBase.php b/core/modules/config_translation/src/Form/ConfigTranslationFormBase.php
index cb49084..42d0b9e 100644
--- a/core/modules/config_translation/src/Form/ConfigTranslationFormBase.php
+++ b/core/modules/config_translation/src/Form/ConfigTranslationFormBase.php
@@ -8,7 +8,9 @@
 namespace Drupal\config_translation\Form;
 
 use Drupal\config_translation\ConfigMapperManagerInterface;
+use Drupal\config_translation\ConfigNamesMapper;
 use Drupal\Core\Config\TypedConfigManagerInterface;
+use Drupal\Core\Render\RendererInterface;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\Core\TypedData\TypedDataInterface;
 use Drupal\Core\Form\BaseFormIdInterface;
@@ -52,6 +54,13 @@
   protected $languageManager;
 
   /**
+   * The renderer.
+   *
+   * @var \Drupal\Core\Render\RendererInterface
+   */
+  protected $renderer;
+
+  /**
    * The language of the configuration translation.
    *
    * @var \Drupal\Core\Language\LanguageInterface
@@ -81,11 +90,13 @@
    *   The configuration mapper manager.
    * @param \Drupal\language\ConfigurableLanguageManagerInterface $language_manager
    *   The configurable language manager.
+   * @param \Drupal\Core\Render\RendererInterface
    */
-  public function __construct(TypedConfigManagerInterface $typed_config_manager, ConfigMapperManagerInterface $config_mapper_manager, ConfigurableLanguageManagerInterface $language_manager) {
+  public function __construct(TypedConfigManagerInterface $typed_config_manager, ConfigMapperManagerInterface $config_mapper_manager, ConfigurableLanguageManagerInterface $language_manager, RendererInterface $renderer) {
     $this->typedConfigManager = $typed_config_manager;
     $this->configMapperManager = $config_mapper_manager;
     $this->languageManager = $language_manager;
+    $this->renderer = $renderer;
   }
 
   /**
@@ -95,7 +106,8 @@ public static function create(ContainerInterface $container) {
     return new static(
       $container->get('config.typed'),
       $container->get('plugin.manager.config_translation.mapper'),
-      $container->get('language_manager')
+      $container->get('language_manager'),
+      $container->get('renderer')
     );
   }
 
@@ -143,7 +155,30 @@ public function buildForm(array $form, FormStateInterface $form_state, RouteMatc
 
     $this->mapper = $mapper;
     $this->language = $language;
-    $this->sourceLanguage = $this->languageManager->getLanguage($this->mapper->getLangcode());
+
+    try {
+      $langcode = $this->mapper->getLangcode();
+    }
+    catch (\RuntimeException $exception) {
+      $message = '';
+      if ($mapper instanceof ConfigNamesMapper) {
+        $items = [];
+        foreach ($mapper->getconfigNames() as $config_name) {
+          $langcode = $mapper->getLangcodeFromConfig($config_name);
+          $items[] = $config_name .': ' . $this->languageManager->getLanguage($langcode)->getName();
+        }
+        $message = [
+          'message' => ['#markup' => t('Configuration objects have different language codes:')],
+          'items' => [
+            '#theme' => 'item_list',
+            '#items' => $items,
+          ]
+        ];
+      }
+      drupal_set_message($this->renderer->renderRoot($message), 'warning');
+    }
+
+    $this->sourceLanguage = $this->languageManager->getLanguage($langcode);
 
     // Get base language configuration to display in the form before setting the
     // language to use for the form. This avoids repetitively settings and
diff --git a/core/modules/node/src/Tests/NodeTypeTranslationTest.php b/core/modules/node/src/Tests/NodeTypeTranslationTest.php
index 10c6865..a473233 100644
--- a/core/modules/node/src/Tests/NodeTypeTranslationTest.php
+++ b/core/modules/node/src/Tests/NodeTypeTranslationTest.php
@@ -24,7 +24,9 @@ class NodeTypeTranslationTest extends WebTestBase {
    * @var array
    */
   public static $modules = array(
+    'block',
     'config_translation',
+    'field_ui',
     'node',
   );
 
@@ -54,6 +56,8 @@ protected function setUp() {
 
     $admin_permissions = array(
       'administer content types',
+      'administer node fields',
+      'administer languages',
       'administer site configuration',
       'administer themes',
       'translate configuration',
@@ -139,6 +143,28 @@ public function testNodeTypeTitleLabelTranslation() {
     $this->assertRaw(t('Edited title'));
     $this->drupalGet("$langcode/node/add/$type");
     $this->assertRaw(t('Translated title'));
+
+    // Add an e-mail field.
+    $this->drupalPostForm("admin/structure/types/manage/$type/fields/add-field", array('new_storage_type' => 'email', 'label' => 'Email', 'field_name' => 'email'), 'Save and continue');
+    $this->drupalPostForm(NULL, array(), 'Save field settings');
+    $this->drupalPostForm(NULL, array(), 'Save settings');
+
+    $type = Unicode::strtolower($this->randomMachineName(16));
+    $name = $this->randomString();
+    $this->drupalCreateContentType(array('type' => $type, 'name' => $name));
+
+    // Set tabs.
+    $this->drupalPlaceBlock('local_tasks_block', array('primary' => TRUE));
+
+    // Change default language.
+    $this->drupalPostForm('admin/config/regional/language', array('site_default_language' => 'es'), 'Save configuration');
+
+    // Try re-using the email field.
+    $this->drupalGet("es/admin/structure/types/manage/$type/fields/add-field");
+    $this->drupalPostForm(NULL, array('existing_storage_name' => 'field_email', 'existing_storage_label' => 'Email'), 'Save and continue');
+    $this->assertResponse(200);
+    $this->drupalGet("es/admin/structure/types/manage/$type/fields/node.$type.field_email/translate");
+    $this->assertResponse(200);
   }
 
 }