diff --git a/core/includes/install.inc b/core/includes/install.inc
index 4c9c60c273c72c861123202f41754d757ee86aa5..f0c329b268a3cf5a3eda84a1a324c8ec4205ef11 100644
--- a/core/includes/install.inc
+++ b/core/includes/install.inc
@@ -700,6 +700,9 @@ function st($string, array $args = array(), array $options = array()) {
       // that multiple files end with the same extension, even if unlikely.
       $files = install_find_translation_files($install_state['parameters']['langcode']);
       if (!empty($files)) {
+        // Register locale classes with the classloader. Locale module is not
+        // yet enabled at this stage, so this is not happening automatically.
+        drupal_classloader_register('locale', drupal_get_path('module', 'locale'));
         $strings = Gettext::filesToArray($install_state['parameters']['langcode'], $files);
       }
     }
diff --git a/core/lib/Drupal/Component/Gettext/PoMemoryWriter.php b/core/lib/Drupal/Component/Gettext/PoMemoryWriter.php
index e304451314bd150e866734d492c20418d63ce4d0..11c53613546b9efe941123282c4bd44dd4ef8213 100644
--- a/core/lib/Drupal/Component/Gettext/PoMemoryWriter.php
+++ b/core/lib/Drupal/Component/Gettext/PoMemoryWriter.php
@@ -34,11 +34,12 @@ function __construct() {
    * Implements Drupal\Component\Gettext\PoWriterInterface::writeItem().
    */
   public function writeItem(PoItem $item) {
-    if (is_array($item->source)) {
-      $item->source = implode(LOCALE_PLURAL_DELIMITER, $item->source);
-      $item->translation = implode(LOCALE_PLURAL_DELIMITER, $item->translation);
+    if (is_array($item->getSource())) {
+      $item->setSource(implode(LOCALE_PLURAL_DELIMITER, $item->getSource()));
+      $item->setTranslation(implode(LOCALE_PLURAL_DELIMITER, $item->getTranslation()));
     }
-    $this->_items[isset($item->context) ? $item->context : ''][$item->source] = $item->translation;
+    $context = $item->getContext();
+    $this->_items[$context != NULL ? $context : ''][$item->getSource()] = $item->getTranslation();
   }
 
   /**