--- /dev/null
+<?php
+
+namespace Drupal\Tests\rest\Functional;
+
+use Psr\Http\Message\ResponseInterface;
+
+/**
+ * Trait for ResourceTestBase subclasses testing $auth=basic_auth + 'language'.
+ *
+ * @see \Drupal\Tests\rest\Functional\BasicAuthResourceTestTrait
+ */
+trait BasicAuthResourceWithInterfaceTranslationTestTrait {
+
+ use BasicAuthResourceTestTrait;
+
+ /**
+ * {@inheritdoc}
+ */
+ protected function assertResponseWhenMissingAuthentication($method, ResponseInterface $response) {
+ // Because BasicAuth::challengeException() relies on the 'system.site'
+ // configuration, and this test installs the 'language' module, all config
+ // may be translated and therefore gets the 'languages:language_interface'
+ // cache context.
+ $expected_page_cache_header_value = $method === 'GET' ? 'MISS' : FALSE;
+ $this->assertResourceErrorResponse(401, 'No authentication credentials provided.', $response, ['4xx-response', 'config:system.site', 'config:user.role.anonymous', 'http_response'], ['languages:language_interface', 'user.roles:anonymous'], $expected_page_cache_header_value, $expected_page_cache_header_value);
+ }
+
+}