diff --git a/core/modules/config_translation/lib/Drupal/config_translation/ConfigMapperManager.php b/core/modules/config_translation/lib/Drupal/config_translation/ConfigMapperManager.php
index b39b44d..0cbcba4 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/ConfigMapperManager.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/ConfigMapperManager.php
@@ -35,6 +35,13 @@ class ConfigMapperManager extends DefaultPluginManager implements ConfigMapperMa
   protected $typedConfigManager;
 
   /**
+   * The theme handler.
+   *
+   * @var \Drupal\Core\Extension\ThemeHandlerInterface
+   */
+  protected $themeHandler;
+
+  /**
    * {@inheritdoc}
    */
   protected $defaults = array(
@@ -78,6 +85,8 @@ public function __construct(CacheBackendInterface $cache_backend, LanguageManage
 
     // Let others alter definitions with hook_config_translation_info_alter().
     $this->moduleHandler = $module_handler;
+    $this->themeHandler = $theme_handler;
+
     $this->alterInfo('config_translation_info');
     $this->setCacheBackend($cache_backend, $language_manager, 'config_translation_info_plugins');
   }
@@ -108,6 +117,28 @@ public function processDefinition(&$definition, $plugin_id) {
   /**
    * {@inheritdoc}
    */
+  protected function findDefinitions() {
+    $definitions = $this->discovery->getDefinitions();
+    foreach ($definitions as $plugin_id => &$definition) {
+      $this->processDefinition($definition, $plugin_id);
+    }
+    if ($this->alterHook) {
+      $this->moduleHandler->alter($this->alterHook, $definitions);
+    }
+
+    // If this plugin was provided by a module that does not exist, remove the
+    // plugin definition.
+    foreach ($definitions as $plugin_id => $plugin_definition) {
+      if (isset($plugin_definition['provider']) && !in_array($plugin_definition['provider'], array('Core', 'Component')) && (!$this->moduleHandler->moduleExists($plugin_definition['provider']) && !in_array($plugin_definition['provider'], array_keys($this->themeHandler->listInfo())))) {
+        unset($definitions[$plugin_id]);
+      }
+    }
+    return $definitions;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function hasTranslatable($name) {
     return $this->findTranslatable($this->typedConfigManager->get($name));
   }
diff --git a/core/modules/system/lib/Drupal/system/Tests/Plugin/PluginTestBase.php b/core/modules/system/lib/Drupal/system/Tests/Plugin/PluginTestBase.php
index 068fe65..50d5736 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Plugin/PluginTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Plugin/PluginTestBase.php
@@ -36,7 +36,8 @@ public function setUp() {
     // - MockBlockManager is used for testing more advanced functionality such
     //   as derivatives and ReflectionFactory.
     $this->testPluginManager = new TestPluginManager();
-    $this->mockBlockManager = new MockBlockManager();$module_handler = new ModuleHandler();
+    $this->mockBlockManager = new MockBlockManager();
+    $module_handler = new ModuleHandler();
     $this->defaultsTestPluginManager = new DefaultsTestPluginManager($module_handler);
 
     // The expected plugin definitions within each manager. Several tests assert