diff --git a/core/lib/Drupal/Core/Entity/ContentEntityBase.php b/core/lib/Drupal/Core/Entity/ContentEntityBase.php
index 4c9b184..f660457 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityBase.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityBase.php
@@ -82,6 +82,13 @@
   protected $langcodeKey;
 
   /**
+   * The default langcode entity key.
+   *
+   * @var string
+   */
+  protected $defaultLangcodeKey;
+
+  /**
    * Language code identifying the entity active language.
    *
    * This is the language field accessors will use to determine which field
@@ -144,6 +151,7 @@ public function __construct(array $values, $entity_type, $bundle = FALSE, $trans
     $this->entityTypeId = $entity_type;
     $this->entityKeys['bundle'] = $bundle ? $bundle : $this->entityTypeId;
     $this->langcodeKey = $this->getEntityType()->getKey('langcode');
+    $this->defaultLangcodeKey = $this->getEntityType()->getKey('default_langcode');
 
     foreach ($values as $key => $value) {
       // If the key matches an existing property set the value to the property
@@ -560,14 +568,34 @@ public function onChange($name) {
       }
     }
 
-    // Update the default internal language cache.
-    if ($name == $this->langcodeKey && $this->isDefaultTranslation()) {
-      $this->setDefaultLangcode();
-      if (isset($this->translations[$this->defaultLangcode])) {
-        $message = String::format('A translation already exists for the specified language (@langcode).', array('@langcode' => $this->defaultLangcode));
-        throw new \InvalidArgumentException($message);
-      }
-      $this->updateFieldLangcodes($this->defaultLangcode);
+    switch ($name) {
+      case $this->langcodeKey:
+        if ($this->isDefaultTranslation()) {
+          // Update the default internal language cache.
+          $this->setDefaultLangcode();
+          if (isset($this->translations[$this->defaultLangcode])) {
+            $message = String::format('A translation already exists for the specified language (@langcode).', array('@langcode' => $this->defaultLangcode));
+            throw new \InvalidArgumentException($message);
+          }
+          $this->updateFieldLangcodes($this->defaultLangcode);
+        }
+        else {
+          // @todo Allow the translation language to be changed. See TODO.
+          $this->get($this->langcodeKey)->setValue($this->activeLangcode, FALSE);
+          $message = String::format('The translation language cannot be changed (@langcode).', array('@langcode' => $this->activeLangcode));
+          throw new \LogicException($message);
+        }
+        break;
+
+      case $this->defaultLangcodeKey:
+        // @todo Use a standard method to make the default_langcode field
+        //   read-only. See TODO.
+        if (isset($this->values[$this->defaultLangcodeKey])) {
+          $this->get($this->defaultLangcodeKey)->setValue($this->isDefaultTranslation(), FALSE);
+          $message = String::format('The default translation flag cannot be changed (@langcode).', array('@langcode' => $this->activeLangcode));
+          throw new \LogicException($message);
+        }
+        break;
     }
   }
 
@@ -702,7 +730,7 @@ public function addTranslation($langcode, array $values = array()) {
       }
     }
     $values[$this->langcodeKey] = $langcode;
-    $values[$this->getEntityType()->getKey('default_langcode')] = FALSE;
+    $values[$this->defaultLangcodeKey] = FALSE;
 
     $this->translations[$langcode]['status'] = static::TRANSLATION_CREATED;
     $translation = $this->getTranslation($langcode);
@@ -710,7 +738,7 @@ public function addTranslation($langcode, array $values = array()) {
 
     foreach ($values as $name => $value) {
       if (isset($definitions[$name]) && $definitions[$name]->isTranslatable()) {
-        $translation->$name = $value;
+        $translation->values[$name][$langcode] = $value;
       }
     }
 
diff --git a/core/modules/system/src/Tests/Entity/EntityTranslationTest.php b/core/modules/system/src/Tests/Entity/EntityTranslationTest.php
index c39b0bb..f646377 100644
--- a/core/modules/system/src/Tests/Entity/EntityTranslationTest.php
+++ b/core/modules/system/src/Tests/Entity/EntityTranslationTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\system\Tests\Entity;
 
 use Drupal\Component\Utility\String;
+use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\entity_test\Entity\EntityTestMulRev;
 use Drupal\language\Entity\ConfigurableLanguage;
@@ -147,6 +148,7 @@ public function testMultilingualProperties() {
    */
   protected function doTestMultilingualProperties($entity_type) {
     $langcode_key = $this->entityManager->getDefinition($entity_type)->getKey('langcode');
+    $default_langcode_key = $this->entityManager->getDefinition($entity_type)->getKey('default_langcode');
     $name = $this->randomMachineName();
     $uid = mt_rand(0, 127);
     $langcode = $this->langcodes[0];
@@ -249,16 +251,16 @@ protected function doTestMultilingualProperties($entity_type) {
     $this->assertEqual(count($entities), 2, format_string('%entity_type: Two entities correctly loaded by name.', array('%entity_type' => $entity_type)));
     // @todo The default language condition should go away in favor of an
     // explicit parameter.
-    $entities = entity_load_multiple_by_properties($entity_type, array('name' => $properties[$langcode]['name'][0], 'default_langcode' => 0));
+    $entities = entity_load_multiple_by_properties($entity_type, array('name' => $properties[$langcode]['name'][0], $default_langcode_key => 0));
     $this->assertEqual(count($entities), 1, format_string('%entity_type: One entity correctly loaded by name translation.', array('%entity_type' => $entity_type)));
     $entities = entity_load_multiple_by_properties($entity_type, array($langcode_key => $default_langcode, 'name' => $name));
     $this->assertEqual(count($entities), 1, format_string('%entity_type: One entity correctly loaded by name and language.', array('%entity_type' => $entity_type)));
 
     $entities = entity_load_multiple_by_properties($entity_type, array($langcode_key => $langcode, 'name' => $properties[$langcode]['name'][0]));
     $this->assertEqual(count($entities), 0, format_string('%entity_type: No entity loaded by name translation specifying the translation language.', array('%entity_type' => $entity_type)));
-    $entities = entity_load_multiple_by_properties($entity_type, array($langcode_key => $langcode, 'name' => $properties[$langcode]['name'][0], 'default_langcode' => 0));
+    $entities = entity_load_multiple_by_properties($entity_type, array($langcode_key => $langcode, 'name' => $properties[$langcode]['name'][0], $default_langcode_key => 0));
     $this->assertEqual(count($entities), 1, format_string('%entity_type: One entity loaded by name translation and language specifying to look for translations.', array('%entity_type' => $entity_type)));
-    $entities = entity_load_multiple_by_properties($entity_type, array('user_id' => $properties[$langcode]['user_id'][0], 'default_langcode' => NULL));
+    $entities = entity_load_multiple_by_properties($entity_type, array('user_id' => $properties[$langcode]['user_id'][0], $default_langcode_key => NULL));
     $this->assertEqual(count($entities), 2, format_string('%entity_type: Two entities loaded by uid without caring about property translatability.', array('%entity_type' => $entity_type)));
 
     // Test property conditions and orders with multiple languages in the same
@@ -313,6 +315,9 @@ protected function doTestEntityTranslationAPI($entity_type) {
     $default_langcode = $this->langcodes[0];
     $langcode = $this->langcodes[1];
     $langcode_key = $this->entityManager->getDefinition($entity_type)->getKey('langcode');
+    $default_langcode_key = $this->entityManager->getDefinition($entity_type)->getKey('default_langcode');
+
+    /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
     $entity = $this->entityManager
       ->getStorage($entity_type)
       ->create(array('name' => $this->randomMachineName(), $langcode_key => LanguageInterface::LANGCODE_NOT_SPECIFIED));
@@ -324,12 +329,13 @@ protected function doTestEntityTranslationAPI($entity_type) {
     // Verify that we obtain the entity object itself when we attempt to
     // retrieve a translation referring to it.
     $translation = $entity->getTranslation($langcode);
-    $this->assertEqual($entity, $translation, 'The translation object corresponding to a non-default language is the entity object itself when the entity is language-neutral.');
+    $this->assertIdentical($entity, $translation, 'The translation object corresponding to a non-default language is the entity object itself when the entity is language-neutral.');
     $entity->{$langcode_key}->value = $default_langcode;
     $translation = $entity->getTranslation($default_langcode);
-    $this->assertEqual($entity, $translation, 'The translation object corresponding to the default language (explicit) is the entity object itself.');
+    $this->assertIdentical($entity, $translation, 'The translation object corresponding to the default language (explicit) is the entity object itself.');
     $translation = $entity->getTranslation(LanguageInterface::LANGCODE_DEFAULT);
-    $this->assertEqual($entity, $translation, 'The translation object corresponding to the default language (implicit) is the entity object itself.');
+    $this->assertIdentical($entity, $translation, 'The translation object corresponding to the default language (implicit) is the entity object itself.');
+    $this->assertTrue($entity->{$default_langcode_key}->value, 'The translation object is the default one.');
 
     // Create a translation and verify that the translation object and the
     // original object behave independently.
@@ -340,18 +346,47 @@ protected function doTestEntityTranslationAPI($entity_type) {
     $this->assertNotIdentical($entity, $translation, 'The entity and the translation object differ from one another.');
     $this->assertTrue($entity->hasTranslation($langcode), 'The new translation exists.');
     $this->assertEqual($translation->language()->getId(), $langcode, 'The translation language matches the specified one.');
+    $this->assertEqual($translation->{$langcode_key}->value, $langcode, 'The translation field language value matches the specified one.');
+    $this->assertFalse($translation->{$default_langcode_key}->value, 'The translation object is not the default one.');
     $this->assertEqual($translation->getUntranslated()->language()->getId(), $default_langcode, 'The original language can still be retrieved.');
     $translation->name->value = $name_translated;
     $this->assertEqual($entity->name->value, $name, 'The original name is retained after setting a translated value.');
     $entity->name->value = $name;
     $this->assertEqual($translation->name->value, $name_translated, 'The translated name is retained after setting the original value.');
 
-    // Save the translation and check that the expecte hooks are fired.
+    // Save the translation and check that the expected hooks are fired.
     $translation->save();
     $hooks = $this->getHooksInfo();
     $this->assertEqual($hooks['entity_translation_insert'], $langcode, 'The generic entity translation insertion hook has fired.');
     $this->assertEqual($hooks[$entity_type . '_translation_insert'], $langcode, 'The entity-type-specific entity translation insertion hook has fired.');
 
+    // Verify that changing translation language causes an exception to be
+    // thrown.
+    $message = 'The translation language cannot be changed.';
+    try {
+      $translation->{$langcode_key}->value = $this->langcodes[2];
+      $this->fail($message);
+    }
+    catch (\LogicException $e) {
+      $this->pass($message);
+    }
+
+    // Verify that changing the default translation flag causes an exception to
+    // be thrown.
+    $message = 'The default translation flag cannot be changed.';
+    foreach ($entity->getTranslationLanguages() as $t_langcode => $language) {
+      $translation = $entity->getTranslation($t_langcode);
+      $default = $translation->isDefaultTranslation();
+      try {
+        $translation->{$default_langcode_key}->value = !$default;
+        $this->fail($message);
+      }
+      catch (\LogicException $e) {
+        $this->pass($message);
+      }
+      $this->assertEqual($translation->{$default_langcode_key}->value, $default);
+    }
+
     // Check that after loading an entity the language is the default one.
     $entity = $this->reloadEntity($entity);
     $this->assertEqual($entity->language()->getId(), $default_langcode, 'The loaded entity is the original one.');
diff --git a/core/modules/system/tests/modules/entity_test/src/Entity/EntityTestMulLangcodeKey.php b/core/modules/system/tests/modules/entity_test/src/Entity/EntityTestMulLangcodeKey.php
index 0b5585b..c50f2c7 100644
--- a/core/modules/system/tests/modules/entity_test/src/Entity/EntityTestMulLangcodeKey.php
+++ b/core/modules/system/tests/modules/entity_test/src/Entity/EntityTestMulLangcodeKey.php
@@ -34,6 +34,7 @@
  *     "bundle" = "type",
  *     "label" = "name",
  *     "langcode" = "custom_langcode_key",
+ *     "default_langcode" = "custom_default_langcode_key",
  *   },
  *   links = {
  *     "canonical" = "/entity_test_mul_langcode_key/manage/{entity_test_mul_langcode_key}",