diff --git a/core/lib/Drupal/Core/Entity/EntityInterface.php b/core/lib/Drupal/Core/Entity/EntityInterface.php
index c0949f7..622c7ee 100644
--- a/core/lib/Drupal/Core/Entity/EntityInterface.php
+++ b/core/lib/Drupal/Core/Entity/EntityInterface.php
@@ -9,7 +9,6 @@
 
 use Drupal\Core\TypedData\AccessibleInterface;
 use Drupal\Core\TypedData\ComplexDataInterface;
-use Drupal\Core\TypedData\IdentifiableInterface;
 use Drupal\Core\TypedData\TranslatableInterface;
 
 /**
@@ -28,7 +27,7 @@
  * @see \Drupal\Core\TypedData\TypedDataManager
  * @see \Drupal\Core\Field\FieldInterface
  */
-interface EntityInterface extends IdentifiableInterface, ComplexDataInterface, AccessibleInterface, TranslatableInterface {
+interface EntityInterface extends ComplexDataInterface, AccessibleInterface, TranslatableInterface {
 
   /**
    * Returns the entity UUID (Universally Unique Identifier).
@@ -42,6 +41,14 @@
   public function uuid();
 
   /**
+   * Returns the identifier.
+   *
+   * @return string|int|null
+   *   The object identifier, or NULL if the object does not yet have an identifier.
+   */
+  public function id();
+
+  /**
    * Returns whether the entity is new.
    *
    * Usually an entity is new if no ID exists for it yet. However, entities may
diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/LanguageReference.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/LanguageReference.php
index 8d143a7..a4c061f 100644
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/LanguageReference.php
+++ b/core/lib/Drupal/Core/Entity/Plugin/DataType/LanguageReference.php
@@ -36,4 +36,12 @@ public function getTargetDefinition() {
       'type' => 'language',
     );
   }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTargetIdentifier() {
+    $language = $this->getTarget();
+    return isset($language) ? $language->id() : NULL;
+  }
 }
diff --git a/core/lib/Drupal/Core/TypedData/DataReferenceBase.php b/core/lib/Drupal/Core/TypedData/DataReferenceBase.php
index 8e67a24..22d8f32 100644
--- a/core/lib/Drupal/Core/TypedData/DataReferenceBase.php
+++ b/core/lib/Drupal/Core/TypedData/DataReferenceBase.php
@@ -56,12 +56,4 @@ public function setValue($value, $notify = TRUE) {
   public function getString() {
     return (string) $this->getType() . ':' . $this->getTargetIdentifier();
   }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getTargetIdentifier() {
-    $target = $this->getTarget();
-    return isset($target) ? $target->id() : NULL;
-  }
 }
diff --git a/core/lib/Drupal/Core/TypedData/IdentifiableInterface.php b/core/lib/Drupal/Core/TypedData/IdentifiableInterface.php
deleted file mode 100644
index 09f8c92..0000000
--- a/core/lib/Drupal/Core/TypedData/IdentifiableInterface.php
+++ /dev/null
@@ -1,22 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\Core\TypedData\IdentifiableInterface.
- */
-
-namespace Drupal\Core\TypedData;
-
-/**
- * Interface for identifiable typed data.
- */
-interface IdentifiableInterface {
-
-  /**
-   * Returns the identifier.
-   *
-   * @return string|int|null
-   *   The object identifier, or NULL if the object does not yet have an identifier.
-   */
-  public function id();
-}
diff --git a/core/lib/Drupal/Core/TypedData/Plugin/DataType/Language.php b/core/lib/Drupal/Core/TypedData/Plugin/DataType/Language.php
index 5ba5b0f..0b5a791 100644
--- a/core/lib/Drupal/Core/TypedData/Plugin/DataType/Language.php
+++ b/core/lib/Drupal/Core/TypedData/Plugin/DataType/Language.php
@@ -10,7 +10,6 @@
 use Drupal\Core\TypedData\Annotation\DataType;
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Language\Language as LanguageObject;
-use Drupal\Core\TypedData\IdentifiableInterface;
 use Drupal\Core\TypedData\TypedData;
 
 /**
@@ -26,7 +25,7 @@
  *   description = @Translation("A language object.")
  * )
  */
-class Language extends TypedData implements IdentifiableInterface {
+class Language extends TypedData {
 
   /**
    * The id of the language.