only in patch2:
unchanged:
--- a/core/modules/rest/tests/src/Unit/EntityResourceValidationTraitTest.php
+++ b/core/modules/rest/tests/src/Unit/EntityResourceValidationTraitTest.php
@@ -3,6 +3,7 @@
 namespace Drupal\Tests\rest\Unit;
 
 use Drupal\Core\Entity\EntityConstraintViolationList;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\node\Entity\Node;
 use Drupal\Tests\UnitTestCase;
 use Drupal\user\Entity\User;
@@ -28,8 +29,12 @@ public function testValidate() {
     $violations->filterByFieldAccess()->shouldBeCalled()->willReturn([]);
     $violations->count()->shouldBeCalled()->willReturn(0);
 
+    $translatable_entity = $this->prophesize(Node::class);
+    $translatable_entity->validate()->shouldBeCalled()->willReturn($violations->reveal());
+
     $entity = $this->prophesize(Node::class);
-    $entity->validate()->shouldBeCalled()->willReturn($violations->reveal());
+    $entity->getTranslationLanguages()->shouldBeCalled()->willReturn(['en' => LanguageInterface::class]);
+    $entity->getTranslation('en')->shouldBeCalled()->willReturn($translatable_entity);
 
     $method->invoke($trait, $entity->reveal());
   }
@@ -57,7 +62,11 @@ public function testFailedValidate() {
       ->method('filterByFieldAccess')
       ->will($this->returnValue([]));
 
-    $entity->validate()->willReturn($violations);
+    $translatable_entity = $this->prophesize(Node::class);
+    $translatable_entity->validate()->shouldBeCalled()->willReturn($violations);
+
+    $entity->getTranslationLanguages()->shouldBeCalled()->willReturn(['en' => LanguageInterface::class]);
+    $entity->getTranslation('en')->shouldBeCalled()->willReturn($translatable_entity);
 
     $trait = $this->getMockForTrait('Drupal\rest\Plugin\rest\resource\EntityResourceValidationTrait');