diff --git a/core/lib/Drupal/Core/Entity/ContentEntityBase.php b/core/lib/Drupal/Core/Entity/ContentEntityBase.php
index b524890..dcf358b 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityBase.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityBase.php
@@ -585,11 +585,13 @@ protected function updateFieldLangcodes($langcode) {
   /**
    * {@inheritdoc}
    */
-  public function onChange($property_name) {
-    if ($property_name == 'langcode') {
-      // Avoid using unset as this unnecessarily triggers magic methods later
-      // on.
+  public function onChange($name) {
+    if ($name == 'langcode') {
       $this->setDefaultLangcode();
+      if (isset($this->translations[$this->defaultLangcode])) {
+        $message = format_string('A translation already exists for the specified language (@langcode).', array('@langcode' => $this->defaultLangcode));
+        throw new \InvalidArgumentException($message);
+      }
       $this->updateFieldLangcodes($this->defaultLangcode);
     }
   }
diff --git a/core/modules/aggregator/aggregator.install b/core/modules/aggregator/aggregator.install
index f891444..b47dc01 100644
--- a/core/modules/aggregator/aggregator.install
+++ b/core/modules/aggregator/aggregator.install
@@ -312,7 +312,7 @@ function aggregator_update_8001() {
     'length' => 12,
     'not null' => TRUE,
     'default' => '',
-    'initial' => Language::LANGCODE_DEFAULT,
+    'initial' => Language::LANGCODE_NOT_SPECIFIED,
   ));
   db_add_field('aggregator_item', 'langcode', array(
     'description' => 'The {language}.langcode of this feed item.',
@@ -320,6 +320,6 @@ function aggregator_update_8001() {
     'length' => 12,
     'not null' => TRUE,
     'default' => '',
-    'initial' => Language::LANGCODE_DEFAULT,
+    'initial' => Language::LANGCODE_NOT_SPECIFIED,
   ));
 }
diff --git a/core/modules/hal/lib/Drupal/hal/Normalizer/FieldNormalizer.php b/core/modules/hal/lib/Drupal/hal/Normalizer/FieldNormalizer.php
index bd3472f..7fe938a 100644
--- a/core/modules/hal/lib/Drupal/hal/Normalizer/FieldNormalizer.php
+++ b/core/modules/hal/lib/Drupal/hal/Normalizer/FieldNormalizer.php
@@ -44,9 +44,9 @@ public function normalize($field, $format = NULL, array $context = array()) {
     // in to the field item normalizer in the context. The langcode is appended
     // to the field item values.
     else {
-      foreach ($entity->getTranslationLanguages() as $lang) {
-        $context['langcode'] = $lang->id == 'und' ? Language::LANGCODE_DEFAULT : $lang->id;
-        $translation = $entity->getTranslation($lang->id);
+      foreach ($entity->getTranslationLanguages() as $language) {
+        $context['langcode'] = $language->id;
+        $translation = $entity->getTranslation($language->id);
         $translated_field = $translation->get($field_name);
         $normalized_field_items = array_merge($normalized_field_items, $this->normalizeFieldItems($translated_field, $format, $context));
       }
diff --git a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityLanguageTestBase.php b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityLanguageTestBase.php
new file mode 100644
index 0000000..cf38de6
--- /dev/null
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityLanguageTestBase.php
@@ -0,0 +1,134 @@
+<?php
+
+/**
+ * @file
+ * Definition of Drupal\system\Tests\Entity\EntityLanguageTestBase.
+ */
+
+namespace Drupal\system\Tests\Entity;
+
+use Drupal\Core\Language\Language;
+use Drupal\field\Field as FieldService;
+
+/**
+ * Base class for language-aware entity tests.
+ */
+abstract class EntityLanguageTestBase extends EntityUnitTestBase {
+
+  protected $langcodes;
+
+  /**
+   * The test field name.
+   *
+   * @var string
+   */
+  protected $field_name;
+
+  /**
+   * The untranslatable test field name.
+   *
+   * @var string
+   */
+  protected $untranslatable_field_name;
+
+  public static $modules = array('language', 'entity_test');
+
+  function setUp() {
+    parent::setUp();
+
+    $this->installSchema('system', 'variable');
+    $this->installSchema('entity_test', array(
+      'entity_test_mul',
+      'entity_test_mul_property_data',
+      'entity_test_rev',
+      'entity_test_rev_revision',
+      'entity_test_mulrev',
+      'entity_test_mulrev_revision',
+      'entity_test_mulrev_property_data',
+      'entity_test_mulrev_property_revision',
+    ));
+    $this->installConfig(array('language'));
+
+    // Create the test field.
+    entity_test_install();
+
+    // Enable translations for the test entity type.
+    $this->state->set('entity_test.translation', TRUE);
+
+    // Create a translatable test field.
+    $this->field_name = drupal_strtolower($this->randomName() . '_field_name');
+
+    // Create an untranslatable test field.
+    $this->untranslatable_field_name = drupal_strtolower($this->randomName() . '_field_name');
+
+    // Create field instances in all entity variations.
+    foreach (entity_test_entity_types() as $entity_type) {
+      entity_create('field_entity', array(
+        'name' => $this->field_name,
+        'entity_type' => $entity_type,
+        'type' => 'text',
+        'cardinality' => 4,
+        'translatable' => TRUE,
+      ))->save();
+      entity_create('field_instance', array(
+        'field_name' => $this->field_name,
+        'entity_type' => $entity_type,
+        'bundle' => $entity_type,
+      ))->save();
+      $this->instance[$entity_type] = field_read_instance($entity_type, $this->field_name, $entity_type);
+
+      entity_create('field_entity', array(
+        'name' => $this->untranslatable_field_name,
+        'entity_type' => $entity_type,
+        'type' => 'text',
+        'cardinality' => 4,
+        'translatable' => FALSE,
+      ))->save();
+      entity_create('field_instance', array(
+        'field_name' => $this->untranslatable_field_name,
+        'entity_type' => $entity_type,
+        'bundle' => $entity_type,
+      ))->save();
+    }
+
+    // Create the default languages.
+    $default_language = language_save(language_default());
+    $languages = language_default_locked_languages($default_language->weight);
+    foreach ($languages as $language) {
+      language_save($language);
+    }
+
+    // Create test languages.
+    $this->langcodes = array();
+    for ($i = 0; $i < 3; ++$i) {
+      $language = new Language(array(
+        'id' => 'l' . $i,
+        'name' => $this->randomString(),
+        'weight' => $i,
+      ));
+      $this->langcodes[$i] = $language->id;
+      language_save($language);
+    }
+  }
+
+  /**
+   * Toggles field translatability.
+   *
+   * @param string $entity_type
+   *   The type of the entity fields are attached to.
+   */
+  protected function toggleFieldTranslatability($entity_type) {
+    $fields = array($this->field_name, $this->untranslatable_field_name);
+    foreach ($fields as $field_name) {
+      $field = FieldService::fieldInfo()->getField($entity_type, $field_name);
+      $translatable = !$field->isFieldTranslatable();
+      $field->set('translatable', $translatable);
+      $field->save();
+      FieldService::fieldInfo()->flush();
+      $field = FieldService::fieldInfo()->getField($entity_type, $field_name);
+      $this->assertEqual($field->isFieldTranslatable(), $translatable, 'Field translatability changed.');
+    }
+    \Drupal::cache('field')->deleteAll();
+  }
+
+}
diff --git a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityTranslationTest.php b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityTranslationTest.php
index eabcdeb..cd0718e 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityTranslationTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityTranslationTest.php
@@ -8,35 +8,13 @@
 namespace Drupal\system\Tests\Entity;
 
 use Drupal\Component\Utility\MapArray;
-use Drupal\Core\Entity\ContentEntityInterface;
-use Drupal\Core\Entity\FieldableDatabaseStorageController;
 use Drupal\Core\Language\Language;
-use Drupal\Core\TypedData\TranslatableInterface;
 use Drupal\entity_test\Entity\EntityTestMulRev;
-use Drupal\field\Field as FieldService;
 
 /**
  * Tests entity translation.
  */
-class EntityTranslationTest extends EntityUnitTestBase {
-
-  protected $langcodes;
-
-  /**
-   * The test field name.
-   *
-   * @var string
-   */
-  protected $field_name;
-
-  /**
-   * The untranslatable test field name.
-   *
-   * @var string
-   */
-  protected $untranslatable_field_name;
-
-  public static $modules = array('language', 'entity_test');
+class EntityTranslationTest extends EntityLanguageTestBase {
 
   public static function getInfo() {
     return array(
@@ -46,84 +24,6 @@ public static function getInfo() {
     );
   }
 
-  function setUp() {
-    parent::setUp();
-
-    $this->installSchema('system', 'variable');
-    $this->installSchema('entity_test', array(
-      'entity_test_mul',
-      'entity_test_mul_property_data',
-      'entity_test_rev',
-      'entity_test_rev_revision',
-      'entity_test_mulrev',
-      'entity_test_mulrev_revision',
-      'entity_test_mulrev_property_data',
-      'entity_test_mulrev_property_revision',
-    ));
-    $this->installConfig(array('language'));
-
-    // Create the test field.
-    entity_test_install();
-
-    // Enable translations for the test entity type.
-    $this->state->set('entity_test.translation', TRUE);
-
-    // Create a translatable test field.
-    $this->field_name = drupal_strtolower($this->randomName() . '_field_name');
-
-    // Create an untranslatable test field.
-    $this->untranslatable_field_name = drupal_strtolower($this->randomName() . '_field_name');
-
-    // Create field instances in all entity variations.
-    foreach (entity_test_entity_types() as $entity_type) {
-      entity_create('field_entity', array(
-        'name' => $this->field_name,
-        'entity_type' => $entity_type,
-        'type' => 'text',
-        'cardinality' => 4,
-        'translatable' => TRUE,
-      ))->save();
-      entity_create('field_instance', array(
-        'field_name' => $this->field_name,
-        'entity_type' => $entity_type,
-        'bundle' => $entity_type,
-      ))->save();
-      $this->instance[$entity_type] = field_read_instance($entity_type, $this->field_name, $entity_type);
-
-      entity_create('field_entity', array(
-        'name' => $this->untranslatable_field_name,
-        'entity_type' => $entity_type,
-        'type' => 'text',
-        'cardinality' => 4,
-        'translatable' => FALSE,
-      ))->save();
-      entity_create('field_instance', array(
-        'field_name' => $this->untranslatable_field_name,
-        'entity_type' => $entity_type,
-        'bundle' => $entity_type,
-      ))->save();
-    }
-
-    // Create the default languages.
-    $default_language = language_save(language_default());
-    $languages = language_default_locked_languages($default_language->weight);
-    foreach ($languages as $language) {
-      language_save($language);
-    }
-
-    // Create test languages.
-    $this->langcodes = array();
-    for ($i = 0; $i < 3; ++$i) {
-      $language = new Language(array(
-        'id' => 'l' . $i,
-        'name' => $this->randomString(),
-        'weight' => $i,
-      ));
-      $this->langcodes[$i] = $language->id;
-      language_save($language);
-    }
-  }
-
   /**
    * Tests language related methods of the Entity class.
    */
@@ -668,116 +568,17 @@ public function testLanguageChange() {
     foreach (array($this->field_name, $this->untranslatable_field_name) as $field_name) {
       $this->assertEqual($entity->get($field_name)->getLangcode(), $langcode, 'Field language works as expected after translating the entity and changing language.');
     }
-  }
 
-  /**
-   * Tests field SQL storage.
-   */
-  public function testFieldSqlStorage() {
-    $entity_type = 'entity_test_mul';
-
-    $controller = $this->entityManager->getStorageController($entity_type);
-    $values = array(
-      $this->field_name => $this->randomName(),
-      $this->untranslatable_field_name => $this->randomName(),
-    );
-    $entity = $controller->create($values);
-    $entity->save();
-
-    // Tests that when changing language field language codes are still correct.
-    $langcode = $this->langcodes[0];
-    $entity->langcode->value = $langcode;
-    $entity->save();
-    $this->assertFieldStorageLangcode($entity, 'Field language successfully changed from language neutral.');
-    $langcode = $this->langcodes[1];
-    $entity->langcode->value = $langcode;
-    $entity->save();
-    $this->assertFieldStorageLangcode($entity, 'Field language successfully changed.');
-    $langcode = Language::LANGCODE_NOT_SPECIFIED;
-    $entity->langcode->value = $langcode;
-    $entity->save();
-    $this->assertFieldStorageLangcode($entity, 'Field language successfully changed to language neutral.');
-
-    // Test that after switching field translatability things keep working as
-    // before.
-    $this->toggleFieldTranslatability($entity_type);
-    $entity = $this->reloadEntity($entity);
-    foreach (array($this->field_name, $this->untranslatable_field_name) as $field_name) {
-      $this->assertEqual($entity->get($field_name)->value, $values[$field_name], 'Field language works as expected after switching translatability.');
+    // Check that setting the default language to an existing translation
+    // language causes an exception to be thrown.
+    $message = 'An exception is thrown when setting the default language to an existing translation language';
+    try {
+      $entity->langcode->value = $this->langcodes[2];
+      $this->fail($message);
     }
-
-    // Test that after disabling field translatability translated values are not
-    // loaded.
-    $this->toggleFieldTranslatability($entity_type);
-    $entity = $this->reloadEntity($entity);
-    $entity->langcode->value = $this->langcodes[0];
-    $translation = $entity->addTranslation($this->langcodes[1]);
-    $translated_value = $this->randomName();
-    $translation->get($this->field_name)->value = $translated_value;
-    $translation->save();
-    $this->toggleFieldTranslatability($entity_type);
-    $entity = $this->reloadEntity($entity);
-    $this->assertEqual($entity->getTranslation($this->langcodes[1])->get($this->field_name)->value, $values[$this->field_name], 'Existing field translations are not loaded for untranslatable fields.');
-  }
-
-  /**
-   * Checks whether field languages are correctly stored for the given entity.
-   *
-   * @param \Drupal\Core\Entity\ContentEntityInterface $entity
-   *   The entity fields are attached to.
-   * @param string $message
-   *   (optional) A message to display with the assertion.
-   */
-  protected function assertFieldStorageLangcode(ContentEntityInterface $entity, $message = '') {
-    $status = TRUE;
-    $entity_type = $entity->entityType();
-    $id = $entity->id();
-    $langcode = $entity->getUntranslated()->language()->id;
-    $fields = array($this->field_name, $this->untranslatable_field_name);
-
-    foreach ($fields as $field_name) {
-      $field = FieldService::fieldInfo()->getField($entity_type, $field_name);
-      $tables = array(
-        FieldableDatabaseStorageController::_fieldTableName($field),
-        FieldableDatabaseStorageController::_fieldRevisionTableName($field),
-      );
-
-      foreach ($tables as $table) {
-        $record = \Drupal::database()
-          ->select($table, 'f')
-          ->fields('f')
-          ->condition('f.entity_id', $id)
-          ->condition('f.revision_id', $id)
-          ->execute()
-          ->fetchObject();
-
-        if ($record->langcode != $langcode) {
-          $status = FALSE;
-          break;
-        }
-      }
+    catch (\InvalidArgumentException $e) {
+      $this->pass($message);
     }
-
-    return $this->assertTrue($status, $message);
   }
 
-  /**
-   * Toggles field translatability.
-   *
-   * @param string $entity_type
-   *   The type of the entity fields are attached to.
-   */
-  protected function toggleFieldTranslatability($entity_type) {
-    $fields = array($this->field_name, $this->untranslatable_field_name);
-    foreach ($fields as $field_name) {
-      $field = FieldService::fieldInfo()->getField($entity_type, $field_name);
-      $translatable = !$field->isFieldTranslatable();
-      $field->set('translatable', $translatable);
-      $field->save();
-      FieldService::fieldInfo()->flush();
-      $field = FieldService::fieldInfo()->getField($entity_type, $field_name);
-      $this->assertEqual($field->isFieldTranslatable(), $translatable, 'Field translatability changed.');
-    }
-    \Drupal::cache('field')->deleteAll();
-  }
 }
diff --git a/core/modules/system/lib/Drupal/system/Tests/Entity/FieldTranslationSqlStorageTest.php b/core/modules/system/lib/Drupal/system/Tests/Entity/FieldTranslationSqlStorageTest.php
new file mode 100644
index 0000000..b6790aa
--- /dev/null
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/FieldTranslationSqlStorageTest.php
@@ -0,0 +1,119 @@
+<?php
+
+/**
+ * @file
+ * Definition of Drupal\system\Tests\Entity\FieldTranslationSqlStorageTest.
+ */
+
+namespace Drupal\system\Tests\Entity;
+
+use Drupal\Core\Entity\ContentEntityInterface;
+use Drupal\Core\Entity\FieldableDatabaseStorageController;
+use Drupal\Core\Language\Language;
+use Drupal\field\Field as FieldService;
+
+/**
+ * Tests entity translation.
+ */
+class FieldTranslationSqlStorageTest extends EntityLanguageTestBase {
+
+  public static function getInfo() {
+    return array(
+      'name'  => 'Field translation SQL storage tests',
+      'description'  => "Test Field translation SQL Storage.",
+      'group' => 'Entity API'
+    );
+  }
+
+  /**
+   * Tests field SQL storage.
+   */
+  public function testFieldSqlStorage() {
+    $entity_type = 'entity_test_mul';
+
+    $controller = $this->entityManager->getStorageController($entity_type);
+    $values = array(
+      $this->field_name => $this->randomName(),
+      $this->untranslatable_field_name => $this->randomName(),
+    );
+    $entity = $controller->create($values);
+    $entity->save();
+
+    // Tests that when changing language field language codes are still correct.
+    $langcode = $this->langcodes[0];
+    $entity->langcode->value = $langcode;
+    $entity->save();
+    $this->assertFieldStorageLangcode($entity, 'Field language successfully changed from language neutral.');
+    $langcode = $this->langcodes[1];
+    $entity->langcode->value = $langcode;
+    $entity->save();
+    $this->assertFieldStorageLangcode($entity, 'Field language successfully changed.');
+    $langcode = Language::LANGCODE_NOT_SPECIFIED;
+    $entity->langcode->value = $langcode;
+    $entity->save();
+    $this->assertFieldStorageLangcode($entity, 'Field language successfully changed to language neutral.');
+
+    // Test that after switching field translatability things keep working as
+    // before.
+    $this->toggleFieldTranslatability($entity_type);
+    $entity = $this->reloadEntity($entity);
+    foreach (array($this->field_name, $this->untranslatable_field_name) as $field_name) {
+      $this->assertEqual($entity->get($field_name)->value, $values[$field_name], 'Field language works as expected after switching translatability.');
+    }
+
+    // Test that after disabling field translatability translated values are not
+    // loaded.
+    $this->toggleFieldTranslatability($entity_type);
+    $entity = $this->reloadEntity($entity);
+    $entity->langcode->value = $this->langcodes[0];
+    $translation = $entity->addTranslation($this->langcodes[1]);
+    $translated_value = $this->randomName();
+    $translation->get($this->field_name)->value = $translated_value;
+    $translation->save();
+    $this->toggleFieldTranslatability($entity_type);
+    $entity = $this->reloadEntity($entity);
+    $this->assertEqual($entity->getTranslation($this->langcodes[1])->get($this->field_name)->value, $values[$this->field_name], 'Existing field translations are not loaded for untranslatable fields.');
+  }
+
+  /**
+   * Checks whether field languages are correctly stored for the given entity.
+   *
+   * @param \Drupal\Core\Entity\ContentEntityInterface $entity
+   *   The entity fields are attached to.
+   * @param string $message
+   *   (optional) A message to display with the assertion.
+   */
+  protected function assertFieldStorageLangcode(ContentEntityInterface $entity, $message = '') {
+    $status = TRUE;
+    $entity_type = $entity->entityType();
+    $id = $entity->id();
+    $langcode = $entity->getUntranslated()->language()->id;
+    $fields = array($this->field_name, $this->untranslatable_field_name);
+
+    foreach ($fields as $field_name) {
+      $field = FieldService::fieldInfo()->getField($entity_type, $field_name);
+      $tables = array(
+        FieldableDatabaseStorageController::_fieldTableName($field),
+        FieldableDatabaseStorageController::_fieldRevisionTableName($field),
+      );
+
+      foreach ($tables as $table) {
+        $record = \Drupal::database()
+          ->select($table, 'f')
+          ->fields('f')
+          ->condition('f.entity_id', $id)
+          ->condition('f.revision_id', $id)
+          ->execute()
+          ->fetchObject();
+
+        if ($record->langcode != $langcode) {
+          $status = FALSE;
+          break;
+        }
+      }
+    }
+
+    return $this->assertTrue($status, $message);
+  }
+
+}