core/modules/ckeditor5/tests/src/Kernel/ValidatorsTest.php | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/core/modules/ckeditor5/tests/src/Kernel/ValidatorsTest.php b/core/modules/ckeditor5/tests/src/Kernel/ValidatorsTest.php
index daf3b5162a..a3f7463985 100644
--- a/core/modules/ckeditor5/tests/src/Kernel/ValidatorsTest.php
+++ b/core/modules/ckeditor5/tests/src/Kernel/ValidatorsTest.php
@@ -668,6 +668,7 @@ public function providerPair(): array {
             'allowed_tags' => [
               '<strong>',
               '<table>',
+              '<span lang>',
             ],
           ],
         ],
@@ -679,6 +680,7 @@ public function providerPair(): array {
       'violations' => [
         'settings.plugins.ckeditor5_sourceEditing.allowed_tags.0' => 'The following tag(s) are already supported by enabled plugins and should not be added to the Source Editing "Manually editable HTML tags" field: <em class="placeholder">Bold (&lt;strong&gt;)</em>.',
         'settings.plugins.ckeditor5_sourceEditing.allowed_tags.1' => 'The following tag(s) are already supported by available plugins and should not be added to the Source Editing "Manually editable HTML tags" field. Instead, enable the following plugins to support these tags: <em class="placeholder">Table (&lt;table&gt;)</em>.',
+        'settings.plugins.ckeditor5_sourceEditing.allowed_tags.2' => 'The following attribute(s) are already supported by enabled plugins and should not be added to the Source Editing "Manually editable HTML tags" field: <em class="placeholder">Language (&lt;span lang&gt;)</em>.',
       ],
     ];
     $data['INVALID some invalid Source Editable tags provided by plugin and another available in a not enabled plugin'] = [