diff --git a/core/modules/rest/src/Plugin/rest/resource/EntityResource.php b/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
index 10874680a6..610bfd5db9 100644
--- a/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
+++ b/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
@@ -6,6 +6,7 @@
 use Drupal\Component\Plugin\PluginManagerInterface;
 use Drupal\Core\Cache\CacheableResponseInterface;
 use Drupal\Core\Config\Entity\ConfigEntityType;
+use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\Entity\FieldableEntityInterface;
 use Drupal\Core\Config\ConfigFactoryInterface;
@@ -180,31 +181,26 @@ public function post(EntityInterface $entity = NULL) {
 
     // Validate the received data before saving.
     $this->validate($entity);
-    try {
-      $entity->save();
-      $this->logger->notice('Created entity %type with ID %id.', ['%type' => $entity->getEntityTypeId(), '%id' => $entity->id()]);
+    $entity->save();
+    $this->logger->notice('Created entity %type with ID %id.', ['%type' => $entity->getEntityTypeId(), '%id' => $entity->id()]);
 
-      // 201 Created responses return the newly created entity in the response
-      // body. These responses are not cacheable, so we add no cacheability
-      // metadata here.
-      $headers = [];
-      if (in_array('canonical', $entity->uriRelationships(), TRUE)) {
-        $url = $entity->urlInfo('canonical', ['absolute' => TRUE])->toString(TRUE);
-        $headers['Location'] = $url->getGeneratedUrl();
-      }
-      return new ModifiedResourceResponse($entity, 201, $headers);
-    }
-    catch (EntityStorageException $e) {
-      throw new HttpException(500, 'Internal Server Error', $e);
+    // 201 Created responses return the newly created entity in the response
+    // body. These responses are not cacheable, so we add no cacheability
+    // metadata here.
+    $headers = [];
+    if (in_array('canonical', $entity->uriRelationships(), TRUE)) {
+      $url = $entity->urlInfo('canonical', ['absolute' => TRUE])->toString(TRUE);
+      $headers['Location'] = $url->getGeneratedUrl();
     }
+    return new ModifiedResourceResponse($entity, 201, $headers);
   }
 
   /**
    * Responds to entity PATCH requests.
    *
-   * @param \Drupal\Core\Entity\EntityInterface $original_entity
+   * @param \Drupal\Core\Entity\ContentEntityInterface $original_entity
    *   The original entity object.
-   * @param \Drupal\Core\Entity\EntityInterface $entity
+   * @param \Drupal\Core\Entity\ContentEntityInterface $entity
    *   The entity.
    *
    * @return \Drupal\rest\ModifiedResourceResponse
@@ -212,7 +208,7 @@ public function post(EntityInterface $entity = NULL) {
    *
    * @throws \Symfony\Component\HttpKernel\Exception\HttpException
    */
-  public function patch(EntityInterface $original_entity, EntityInterface $entity = NULL) {
+  public function patch(ContentEntityInterface $original_entity, ContentEntityInterface $entity = NULL) {
     if ($entity == NULL) {
       throw new BadRequestHttpException('No entity content received.');
     }
@@ -227,41 +223,41 @@ public function patch(EntityInterface $original_entity, EntityInterface $entity
 
     // Overwrite the received fields.
     foreach ($entity->_restSubmittedFields as $field_name) {
-      $field = $entity->get($field_name);
-      $original_field = $original_entity->get($field_name);
+      foreach ($entity->getTranslationLanguages() as $langcode => $language) {
+        if (!$original_entity->hasTranslation($langcode)) {
+          $original_entity->addTranslation($langcode, $original_entity->toArray());
+        }
+        $field = $entity->getTranslation($langcode)->get($field_name);
+        $original_field = $original_entity->getTranslation($langcode)->get($field_name);
 
-      // If the user has access to view the field, we need to check update
-      // access regardless of the field value to avoid information disclosure.
-      // (Otherwise the user may try PATCHing with value after value, until they
-      // send the current value for the field, and then they won't get a 403
-      // response anymore, which indicates that the value they sent in the PATCH
-      // request body matches the current value.)
-      if (!$original_field->access('view')) {
-        if (!$original_field->access('edit')) {
+        // If the user has access to view the field, we need to check update
+        // access regardless of the field value to avoid information disclosure.
+        // (Otherwise the user may try PATCHing with value after value, until they
+        // send the current value for the field, and then they won't get a 403
+        // response anymore, which indicates that the value they sent in the PATCH
+        // request body matches the current value.)
+        if (!$original_field->access('view')) {
+          if (!$original_field->access('edit')) {
+            throw new AccessDeniedHttpException("Access denied on updating field '$field_name'.");
+          }
+        }
+        // Check access for all received fields, but only if they are being
+        // changed. The bundle of an entity, for example, must be provided for
+        // denormalization to succeed, but it may not be changed.
+        elseif (!$original_field->equals($field) && !$original_field->access('edit')) {
           throw new AccessDeniedHttpException("Access denied on updating field '$field_name'.");
         }
+        $original_entity->getTranslation($langcode)->set($field_name, $field->getValue());
       }
-      // Check access for all received fields, but only if they are being
-      // changed. The bundle of an entity, for example, must be provided for
-      // denormalization to succeed, but it may not be changed.
-      elseif (!$original_field->equals($field) && !$original_field->access('edit')) {
-        throw new AccessDeniedHttpException("Access denied on updating field '$field_name'.");
-      }
-      $original_entity->set($field_name, $field->getValue());
     }
 
     // Validate the received data before saving.
     $this->validate($original_entity);
-    try {
-      $original_entity->save();
-      $this->logger->notice('Updated entity %type with ID %id.', ['%type' => $original_entity->getEntityTypeId(), '%id' => $original_entity->id()]);
+    $original_entity->save();
+    $this->logger->notice('Updated entity %type with ID %id.', ['%type' => $original_entity->getEntityTypeId(), '%id' => $original_entity->id()]);
 
-      // Return the updated entity in the response body.
-      return new ModifiedResourceResponse($original_entity, 200);
-    }
-    catch (EntityStorageException $e) {
-      throw new HttpException(500, 'Internal Server Error', $e);
-    }
+    // Return the updated entity in the response body.
+    return new ModifiedResourceResponse($original_entity, 200);
   }
 
   /**
diff --git a/core/modules/rest/src/Plugin/rest/resource/EntityResourceValidationTrait.php b/core/modules/rest/src/Plugin/rest/resource/EntityResourceValidationTrait.php
index 09b4b64bae..a769b6b6e3 100644
--- a/core/modules/rest/src/Plugin/rest/resource/EntityResourceValidationTrait.php
+++ b/core/modules/rest/src/Plugin/rest/resource/EntityResourceValidationTrait.php
@@ -3,7 +3,7 @@
 namespace Drupal\rest\Plugin\rest\resource;
 
 use Drupal\Component\Render\PlainTextOutput;
-use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\Core\Entity\FieldableEntityInterface;
 use Symfony\Component\HttpKernel\Exception\UnprocessableEntityHttpException;
 
@@ -16,31 +16,31 @@
   /**
    * Verifies that the whole entity does not violate any validation constraints.
    *
-   * @param \Drupal\Core\Entity\EntityInterface $entity
+   * @param \Drupal\Core\Entity\ContentEntityInterface $entity
    *   The entity to validate.
    *
    * @throws \Symfony\Component\HttpKernel\Exception\UnprocessableEntityHttpException
    *   If validation errors are found.
    */
-  protected function validate(EntityInterface $entity) {
+  protected function validate(ContentEntityInterface $entity) {
     // @todo Remove when https://www.drupal.org/node/2164373 is committed.
     if (!$entity instanceof FieldableEntityInterface) {
       return;
     }
-    $violations = $entity->validate();
-
-    // Remove violations of inaccessible fields as they cannot stem from our
-    // changes.
-    $violations->filterByFieldAccess();
-
-    if ($violations->count() > 0) {
-      $message = "Unprocessable Entity: validation failed.\n";
-      foreach ($violations as $violation) {
-        // We strip every HTML from the error message to have a nicer to read
-        // message on REST responses.
-        $message .= $violation->getPropertyPath() . ': ' . PlainTextOutput::renderFromHtml($violation->getMessage()) . "\n";
+    foreach ($entity->getTranslationLanguages() as $langcode => $language) {
+      $violations = $entity->getTranslation($langcode)->validate();
+      // Remove violations of inaccessible fields as they cannot stem from our
+      // changes.
+      $violations->filterByFieldAccess();
+      if ($violations->count() > 0) {
+        $message = "Unprocessable Entity: validation failed.\n";
+        foreach ($violations as $violation) {
+          // We strip every HTML from the error message to have a nicer to read
+          // message on REST responses.
+          $message .= $violation->getPropertyPath() . ': ' . PlainTextOutput::renderFromHtml($violation->getMessage()) . "\n";
+        }
+        throw new UnprocessableEntityHttpException($message);
       }
-      throw new UnprocessableEntityHttpException($message);
     }
   }
 
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/Comment/CommentResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/Comment/CommentResourceTestBase.php
index 5b5101445a..037bb3b606 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/Comment/CommentResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/Comment/CommentResourceTestBase.php
@@ -277,8 +277,8 @@ public function testPostDxWithoutCriticalBaseFields() {
     $response = $this->request('POST', $url, $request_options);
     // @todo Uncomment, remove next 3 lines in https://www.drupal.org/node/2820364.
     $this->assertSame(500, $response->getStatusCode());
-    $this->assertSame(['text/plain; charset=UTF-8'], $response->getHeader('Content-Type'));
-    $this->assertStringStartsWith('The website encountered an unexpected error. Please try again later.</br></br><em class="placeholder">Symfony\Component\HttpKernel\Exception\HttpException</em>: Internal Server Error in <em class="placeholder">Drupal\rest\Plugin\rest\resource\EntityResource-&gt;post()</em>', (string) $response->getBody());
+    $this->assertSame(['application/json'], $response->getHeader('Content-Type'));
+    $this->assertSame('{"message":"A fatal error occurred: The \u0022\u0022 entity type does not exist."}', (string) $response->getBody());
     //$this->assertResourceErrorResponse(422, "Unprocessable Entity: validation failed.\nentity_type: This value should not be null.\n", $response);
 
     // DX: 422 when missing 'entity_id' field.
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
index 72589bd3b8..5753c85942 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -473,12 +473,16 @@ public function testGet() {
     if ($this->entity->getEntityType()->getLinkTemplates()) {
       $this->assertArrayHasKey('Link', $response->getHeaders());
       $link_relation_type_manager = $this->container->get('plugin.manager.link_relation_type');
-      $expected_link_relation_headers = array_map(function ($relation_name) use ($link_relation_type_manager) {
+      $expected_link_relation_headers = array_filter(array_map(function ($relation_name) use ($link_relation_type_manager) {
+        // @todo What to do about content_translation link relationships?
+        if (strpos($relation_name, 'drupal:content-translation') !== FALSE) {
+          return FALSE;
+        }
         $link_relation_type = $link_relation_type_manager->createInstance($relation_name);
         return $link_relation_type->isRegistered()
           ? $link_relation_type->getRegisteredName()
           : $link_relation_type->getExtensionUri();
-      }, array_keys($this->entity->getEntityType()->getLinkTemplates()));
+      }, array_keys($this->entity->getEntityType()->getLinkTemplates())));
       $parse_rel_from_link_header = function ($value) use ($link_relation_type_manager) {
         $matches = [];
         if (preg_match('/rel="([^"]+)"/', $value, $matches) === 1) {