diff -u b/core/lib/Drupal/Core/Entity/EntityChangedInterface.php b/core/lib/Drupal/Core/Entity/EntityChangedInterface.php
--- b/core/lib/Drupal/Core/Entity/EntityChangedInterface.php
+++ b/core/lib/Drupal/Core/Entity/EntityChangedInterface.php
@@ -22,8 +22,7 @@
 interface EntityChangedInterface {
 
   /**
-   * Returns the timestamp of the last entity change of the current
-   * translation.
+   * Returns the timestamp of the last entity change for current translation.
    *
    * @return int
    *   The timestamp of the last entity save operation.
diff -u b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/ChangedItem.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/ChangedItem.php
--- b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/ChangedItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/ChangedItem.php
@@ -52,9 +52,9 @@
         if ($this->getFieldDefinition()->isTranslatable()) {
           $original = $original->getTranslation($entity->language()->getId());
         }
-        // If the timestamp has not been set explicitly auto detect a modification
-        // of the current translation and set the timestamp if needed.
-        // An example of setting the timestamp explicitly is
+        // If the timestamp has not been set explicitly auto detect a
+        // modification of the current translation and set the timestamp if
+        // needed. An example of setting the timestamp explicitly is
         // \Drupal\content_translation\ContentTranslationMetadataWrapperInterface::setChangedTime()
         if ($this->value == $original->{$field_name}->value) {
           foreach ($entity->getFieldDefinitions() as $other_field_definition) {
diff -u b/core/modules/comment/src/CommentStatistics.php b/core/modules/comment/src/CommentStatistics.php
--- b/core/modules/comment/src/CommentStatistics.php
+++ b/core/modules/comment/src/CommentStatistics.php
@@ -126,7 +126,6 @@
       }
       // Default to REQUEST_TIME when entity does not have a changed property.
       $last_comment_timestamp = REQUEST_TIME;
-      // @todo make comment statistics language aware.
       if ($entity instanceof EntityChangedInterface) {
         $last_comment_timestamp = $entity->getChangedTimeAcrossTranslations();
       }
diff -u b/core/modules/content_translation/src/ContentTranslationMetadataWrapperInterface.php b/core/modules/content_translation/src/ContentTranslationMetadataWrapperInterface.php
--- b/core/modules/content_translation/src/ContentTranslationMetadataWrapperInterface.php
+++ b/core/modules/content_translation/src/ContentTranslationMetadataWrapperInterface.php
@@ -108,8 +108,7 @@
   public function setCreatedTime($timestamp);
 
   /**
-   * Returns the timestamp of the last entity change of the current
-   * translation.
+   * Returns the timestamp of the last entity change from current translation.
    *
    * @return int
    *   The timestamp of the last entity save operation.
diff -u b/core/modules/content_translation/src/Tests/ContentTranslationUITest.php b/core/modules/content_translation/src/Tests/ContentTranslationUITest.php
--- b/core/modules/content_translation/src/Tests/ContentTranslationUITest.php
+++ b/core/modules/content_translation/src/Tests/ContentTranslationUITest.php
@@ -400,8 +400,6 @@
 
         $langcode = $language->getId();
 
-        // Set the custom translatable field and the revision log to predictable
-        // values containing a counter.
         $edit = array(
           $this->fieldName . '[0][value]' => $this->randomString(),
         );
@@ -415,9 +413,9 @@
         );
 
         if ($i > 1) {
-          // Because the base of this test created the translations
-          // without a sleep command, the changed timestamps might not differ
-          // until the second run of that loop.
+          // Because the base of this test created the translations without a
+          // sleep command, the changed timestamps might not differ until the
+          // second run of that loop.
           $timestamps = array();
           foreach ($entity->getTranslationLanguages() as $language) {
             $next_timestamp = $entity->getTranslation($language->getId())
diff -u b/core/modules/node/node.module b/core/modules/node/node.module
--- b/core/modules/node/node.module
+++ b/core/modules/node/node.module
@@ -741,7 +741,7 @@
  * @param $nid
  *   The ID of a node.
  * @param string $langcode
- *   (optional) The language the node has been last modified in. If omitted the
+ *   (optional) The language to get the last changed time for. If omitted the
  *   last changed time across all translations will be returned.
  *
  * @return string
diff -u b/core/modules/node/src/Tests/NodeSaveTest.php b/core/modules/node/src/Tests/NodeSaveTest.php
--- b/core/modules/node/src/Tests/NodeSaveTest.php
+++ b/core/modules/node/src/Tests/NodeSaveTest.php
@@ -130,9 +130,9 @@
     $node->save();
     $node = $this->drupalGetNodeByTitle($edit['title'], TRUE);
     $this->assertEqual($node->getCreatedTime(), 979534800, 'Updating a node uses user-set "created" timestamp.');
-    // Allowing setting changed timestamps is required see
+    // Allowing setting changed timestamps is required, see
     // Drupal\content_translation\ContentTranslationMetadataWrapper::setChangedTime($timestamp)
-    // for example
+    // for example.
     $this->assertEqual($node->getChangedTime(), 280299600, 'Updating a node uses user-set "changed" timestamp.');
   }
 
diff -u b/core/modules/system/src/Tests/Entity/ContentEntityChangedTest.php b/core/modules/system/src/Tests/Entity/ContentEntityChangedTest.php
--- b/core/modules/system/src/Tests/Entity/ContentEntityChangedTest.php
+++ b/core/modules/system/src/Tests/Entity/ContentEntityChangedTest.php
@@ -58,8 +58,8 @@
       'Changed time of original language is valid.'
     );
 
-    // We can't assert equality here because the created time is set to
-    // REQUEST_TIME while instances of ChangedTestItem use the current
+    // We can't assert equality here because the created time is set to the
+    // request time, while instances of ChangedTestItem use the current
     // timestamp every time.
     $this->assertTrue(
       ($entity->getChangedTime() >= $entity->get('created')->value) &&
@@ -148,10 +148,9 @@
       'Changed time of the German translation did not change.'
     );
 
-    // Final state: changed time of original language (en) is newer than
-    // the changed time of the German translation.
-    // Now try some entity queries.
-
+    // Current state: changed time of original language (en) is newer than the
+    // changed time of the German translation. Test that entity queries work as
+    // expected.
     $entity_query_service = $this->container->get('entity.query');
 
     $query = $entity_query_service->get('entity_test_mul_changed');
@@ -175,7 +174,7 @@
 
     $this->assertTrue(
       empty($ids),
-      'There\'s no original entity stored using the changed time of the German translation.'
+      'There\'s no original entity stored having the changed time of the German translation.'
     );
 
     $query = $entity_query_service->get('entity_test_mul_changed');
@@ -199,7 +198,7 @@
 
     $this->assertTrue(
       empty($ids),
-      'There\'s no German translation stored using the changed time of the original language.'
+      'There\'s no German translation stored having the changed time of the original language.'
     );
 
     $query = $entity_query_service->get('entity_test_mul_changed');
@@ -255,8 +254,8 @@
       'Changed time of original language is valid.'
     );
 
-    // We can't assert equality here because the created time is set to
-    // REQUEST_TIME while instances of ChangedTestItem use the current
+    // We can't assert equality here because the created time is set to the
+    // request time while instances of ChangedTestItem use the current
     // timestamp every time.
     $this->assertTrue(
       ($entity->getChangedTime() >= $entity->get('created')->value) &&
@@ -274,7 +273,7 @@
     $entity->setNewRevision();
     // Save entity without any changes but create new revision.
     $entity->save();
-
+    // A new revision without any changes should not set a new changed time.
     $this->assertEqual(
       $entity->getChangedTime(), $changed_en,
       'Changed time of original language did not change.'
diff -u b/core/modules/system/tests/modules/entity_test/src/Plugin/Field/FieldType/ChangedTestItem.php b/core/modules/system/tests/modules/entity_test/src/Plugin/Field/FieldType/ChangedTestItem.php
--- b/core/modules/system/tests/modules/entity_test/src/Plugin/Field/FieldType/ChangedTestItem.php
+++ b/core/modules/system/tests/modules/entity_test/src/Plugin/Field/FieldType/ChangedTestItem.php
@@ -33,6 +33,10 @@
     parent::preSave();
 
     if ($this->value == REQUEST_TIME) {
+      // During a test the request time is immutable. To allow tests of the
+      // algorithm of
+      // Drupal\Core\Field\Plugin\Field\FieldType\ChangedItem::preSave() we need
+      // to set a real time value here.
       $this->value = time();
     }
   }