diff -u b/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampFormatter.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampFormatter.php
--- b/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampFormatter.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampFormatter.php
@@ -82,7 +82,7 @@
       $configuration['view_mode'],
       $configuration['third_party_settings'],
       $container->get('date.formatter'),
-      $container->get('entity_type.manager')->getStorage('date_format')
+      $container->get('entity.manager')->getStorage('date_format')
     );
   }
 
@@ -91,11 +91,12 @@
    */
   public static function defaultSettings() {
     return [
-      'date_format' => 'medium',
-      'custom_date_format' => '',
-      'timezone' => '',
-      'show_prefix_label' => FALSE,
-    ] + parent::defaultSettings();
+        'date_format' => 'medium',
+        'custom_date_format' => '',
+        'timezone' => '',
+        'show_prefix_label' => FALSE,
+        'prefix_label' => 'Authored on: '
+      ] + parent::defaultSettings();
   }
 
   /**
@@ -114,11 +115,17 @@
 
     $elements['show_prefix_label'] = [
       '#type' => 'checkbox',
-      '#title' => $this->t('Show the "On" prefix'),
+      '#title' => $this->t('Show prefix'),
       '#description' => $this->t('Displays a prefix "on" before the content creation date.'),
       '#default_value' => $this->getSetting('show_prefix_label'),
     ];
 
+    $elements['prefix_label'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('Label for prefix'),
+      '#default_value' => $this->getSetting('prefix_label'),
+    ];
+
     $elements['date_format'] = [
       '#type' => 'select',
       '#title' => $this->t('Date format'),
@@ -152,12 +159,12 @@
    */
   public function settingsSummary() {
     $summary = parent::settingsSummary();
-
+    $prefix_label = $this->getSetting('prefix_label');
     if ($this->getSetting('show_prefix_label')) {
-      $summary[] = $this->t('The "on" creation date prefix is displayed.');
+      $summary[] = $this->t('The "@prefix" creation date prefix is displayed.', ['@prefix' => $prefix_label]);
     }
     else {
-      $summary[] = $this->t('The "on" creation date prefix is hidden.');
+      $summary[] = $this->t('The "@prefix" creation date prefix is hidden.', ['@prefix' => $prefix_label]);
     }
     $date_format = $this->getSetting('date_format');
     $summary[] = $this->t('Date format: @date_format', ['@date_format' => $date_format]);
@@ -198,10 +205,10 @@
         '#markup' => $this->dateFormatter->format($item->value, $date_format, $custom_date_format, $timezone, $langcode),
       ];
       if ($this->getSetting('show_prefix_label')) {
-        $elements[$delta]['#prefix'] = $this->t('on ');
+        // Use translation for manual label.
+        $elements[$delta]['#prefix'] = $this->t($this->getSetting('prefix_label'));
       }
     }
-
     return $elements;
   }
 
diff -u b/core/modules/node/tests/src/Functional/NodeCreationTest.php b/core/modules/node/tests/src/Functional/NodeCreationTest.php
--- b/core/modules/node/tests/src/Functional/NodeCreationTest.php
+++ b/core/modules/node/tests/src/Functional/NodeCreationTest.php
@@ -22,16 +22,12 @@
    *
    * @var array
    */
-  public static $modules = ['node_test_exception', 'dblog', 'test_page_test', 'field_ui'];
+  public static $modules = ['node_test_exception', 'dblog', 'test_page_test'];
 
   protected function setUp() {
     parent::setUp();
 
-    $web_user = $this->drupalCreateUser([
-      'create page content',
-      'edit own page content',
-      'administer node display',
-    ]);
+    $web_user = $this->drupalCreateUser(['create page content', 'edit own page content']);
     $this->drupalLogin($web_user);
   }
 
diff -u b/core/modules/rdf/tests/src/Functional/StandardProfileTest.php b/core/modules/rdf/tests/src/Functional/StandardProfileTest.php
--- b/core/modules/rdf/tests/src/Functional/StandardProfileTest.php
+++ b/core/modules/rdf/tests/src/Functional/StandardProfileTest.php
@@ -98,14 +98,14 @@
   protected $articleCommentUri;
 
   /**
-   * @var array
+   * @var string
    */
-  public static $modules  = ['field_ui'];
+  protected $articleCommentUri;
 
   /**
-   * @var string
+   * @var array
    */
-  protected $articleCommentUri;
+  public static $modules  = ['field_ui'];
 
   /**
    * @var string