diff --git a/core/lib/Drupal/Core/Entity/EntityManager.php b/core/lib/Drupal/Core/Entity/EntityManager.php
index b07795f..db52530 100644
--- a/core/lib/Drupal/Core/Entity/EntityManager.php
+++ b/core/lib/Drupal/Core/Entity/EntityManager.php
@@ -371,11 +371,11 @@ public function getFieldDefinitions($entity_type, $bundle = NULL) {
             if (is_array($definition)) {
               $definition = FieldDefinition::createFromOldStyleDefinition($definition);
             }
-            // For manually defined fields, make sure the field name is set.
+            // Automatically set the field-name for non-configurable fields.
             if ($definition instanceof FieldDefinition) {
               $definition->setFieldName($field_name);
             }
-            // Ensure ID and langcode fields are never made translatable.
+            // Ensure all untranslatable fields are not defined as translatable.
             if (isset($untranslatable_fields[$field_name]) && $definition->isFieldTranslatable()) {
               throw new \LogicException(format_string('The @field field cannot be translatable.', array('@field' => $definition->getFieldLabel())));
             }
diff --git a/core/lib/Drupal/Core/Field/Annotation/FieldType.php b/core/lib/Drupal/Core/Field/Annotation/FieldType.php
index dc7e32b..67f64bc 100644
--- a/core/lib/Drupal/Core/Field/Annotation/FieldType.php
+++ b/core/lib/Drupal/Core/Field/Annotation/FieldType.php
@@ -119,4 +119,14 @@ class FieldType extends DataType {
    */
   public $list_type = 'field_item_list';
 
+  /**
+   * The typed data class used for wrapping multiple data items of the type.
+   * Must implement the \Drupal\Core\TypedData\ListInterface.
+   *
+   * @todo Right now, $list_class support is for backwards compatiblity only.
+   * After moving all usages to $list_type, remove this.
+   *
+   * @var string
+   */
+  public $list_class = '\Drupal\Core\Field\Plugin\DataType\FieldItemList';
 }
diff --git a/core/lib/Drupal/Core/Field/FieldDefinitionInterface.php b/core/lib/Drupal/Core/Field/FieldDefinitionInterface.php
index e5b233b..4dca17a 100644
--- a/core/lib/Drupal/Core/Field/FieldDefinitionInterface.php
+++ b/core/lib/Drupal/Core/Field/FieldDefinitionInterface.php
@@ -14,10 +14,9 @@
  * Defines an interface for entity field definitions.
  *
  * An entity field is a data object that holds the values of a particular field
- * for a particular entity (see
- * \Drupal\Core\Field\FieldItemListInterface). For example, $node_1->body
- * and $node_2->body contain different data and therefore are different field
- * objects.
+ * for a particular entity (see \Drupal\Core\Field\FieldItemListInterface). For
+ * example, $node_1->body and $node_2->body contain different data and therefore
+ * are different field objects.
  *
  * In contrast, an entity field *definition* is an object that returns
  * information *about* a field (e.g., its type and settings) rather than its
diff --git a/core/lib/Drupal/Core/Field/FieldItemBase.php b/core/lib/Drupal/Core/Field/FieldItemBase.php
index 70ff483..4645936 100644
--- a/core/lib/Drupal/Core/Field/FieldItemBase.php
+++ b/core/lib/Drupal/Core/Field/FieldItemBase.php
@@ -8,8 +8,6 @@
 namespace Drupal\Core\Field;
 
 use Drupal\Core\Entity\EntityInterface;
-use Drupal\Core\TypedData\DataDefinition;
-use Drupal\Core\TypedData\DataDefinitionInterface;
 use Drupal\Core\TypedData\Plugin\DataType\Map;
 use Drupal\Core\TypedData\TypedDataInterface;
 use Drupal\user;
@@ -25,13 +23,6 @@
 abstract class FieldItemBase extends Map implements FieldItemInterface {
 
   /**
-   * The field's definition.
-   *
-   * @var \Drupal\Core\Field\FieldDefinitionInterface
-   */
-  protected $definition;
-
-  /**
    * Overrides \Drupal\Core\TypedData\TypedData::__construct().
    */
   public function __construct($definition, $name = NULL, TypedDataInterface $parent = NULL) {
diff --git a/core/lib/Drupal/Core/Field/Plugin/DataType/FieldItemList.php b/core/lib/Drupal/Core/Field/Plugin/DataType/FieldItemList.php
index 31ec4e1..93c83ba 100644
--- a/core/lib/Drupal/Core/Field/Plugin/DataType/FieldItemList.php
+++ b/core/lib/Drupal/Core/Field/Plugin/DataType/FieldItemList.php
@@ -44,7 +44,7 @@ class FieldItemList extends ItemList implements FieldItemListInterface {
   protected $langcode = Language::LANGCODE_DEFAULT;
 
   /**
-   * Overrides TypedData::__construct().
+   * {@inheritdoc}
    */
   public function __construct($definition, $name = NULL, TypedDataInterface $parent = NULL) {
     parent::__construct($definition, $name, $parent);
diff --git a/core/lib/Drupal/Core/TypedData/TypedData.php b/core/lib/Drupal/Core/TypedData/TypedData.php
index acfa4ea..6597f3c 100644
--- a/core/lib/Drupal/Core/TypedData/TypedData.php
+++ b/core/lib/Drupal/Core/TypedData/TypedData.php
@@ -51,6 +51,10 @@
    *   root of a typed data tree. Defaults to NULL.
    *
    * @see \Drupal\Core\TypedData\TypedDataManager::create()
+   *
+   * @todo When \Drupal\Core\Config\TypedConfigManager has been fixed to use
+   *   class-based definitions, type-hint $definition to
+   *   DataDefinitionInterface.
    */
   public function __construct($definition, $name = NULL, TypedDataInterface $parent = NULL) {
     $this->definition = $definition;
diff --git a/core/modules/content_translation/content_translation.admin.inc b/core/modules/content_translation/content_translation.admin.inc
index 37e4a6b..c89c6ec 100644
--- a/core/modules/content_translation/content_translation.admin.inc
+++ b/core/modules/content_translation/content_translation.admin.inc
@@ -122,7 +122,7 @@ function _content_translation_form_language_content_settings_form_alter(array &$
             // fields support translation. Whether they are actually enabled is
             // determined through our settings. As a consequence only fields
             // that support translation can be enabled or disabled.
-            elseif (isset($field_settings[$field_name]) || !empty($definition['translatable'])) {
+            elseif (isset($field_settings[$field_name]) || $definition->isFieldTranslatable()) {
               $form['settings'][$entity_type][$bundle]['fields'][$field_name] = array(
                 '#label' => $definition['label'],
                 '#type' => 'checkbox',
diff --git a/core/modules/field/field.deprecated.inc b/core/modules/field/field.deprecated.inc
index 5c213dd..2bedb65 100644
--- a/core/modules/field/field.deprecated.inc
+++ b/core/modules/field/field.deprecated.inc
@@ -926,13 +926,13 @@ function field_language(EntityInterface $entity, $field_name = NULL, $langcode =
   if (!isset($field_name)) {
     $display_langcodes = array();
     foreach ($definitions as $name => $definition) {
-      if (!empty($definition['configurable'])) {
+      if ($definition->isFieldConfigurable()) {
         $display_langcodes[$name] = $translatable ? $langcode : Language::LANGCODE_NOT_SPECIFIED;
       }
     }
     return $display_langcodes;
   }
-  elseif (!empty($definitions[$field_name]['configurable'])) {
+  elseif ($definitions[$field_name]>isFieldConfigurable()) {
     return $translatable ? $langcode : Language::LANGCODE_NOT_SPECIFIED;
   }
 }
diff --git a/core/modules/field/field.module b/core/modules/field/field.module
index 9c46f5b..73ac825 100644
--- a/core/modules/field/field.module
+++ b/core/modules/field/field.module
@@ -194,8 +194,9 @@ function field_entity_field_info($entity_type) {
 
   foreach (field_info_instances($entity_type) as $bundle_name => $instances) {
     $optional = $bundle_name != $entity_type;
-    // @todo: Improve hook_entity_field_info() so that it can take field
-    // instance also.
+    // @todo: Improve hook_entity_field_info() to allow per-bundle field
+    // definitions, such that we can pass on field instances as field
+    // definitions here.
 
     foreach ($instances as $field_name => $instance) {
       if ($optional) {
diff --git a/core/modules/locale/lib/Drupal/locale/LocaleTypedConfig.php b/core/modules/locale/lib/Drupal/locale/LocaleTypedConfig.php
index 4abf5d3..7be07a9 100644
--- a/core/modules/locale/lib/Drupal/locale/LocaleTypedConfig.php
+++ b/core/modules/locale/lib/Drupal/locale/LocaleTypedConfig.php
@@ -11,7 +11,6 @@
 use Drupal\Core\TypedData\ContextAwareInterface;
 use Drupal\Core\Config\Schema\Element;
 use Drupal\Core\Config\Schema\ArrayElement;
-use Drupal\Core\TypedData\DataDefinitionInterface;
 
 /**
  * Defines the locale configuration wrapper object.