diff --git a/composer.lock b/composer.lock
index fdef57dabe..f61110aceb 100644
--- a/composer.lock
+++ b/composer.lock
@@ -534,7 +534,7 @@
             "dist": {
                 "type": "path",
                 "url": "core",
-                "reference": "107b1d4f65408eb2844facd227005517de15343b"
+                "reference": "1878827866afdec864cb4652a3d8b813d970f710"
             },
             "require": {
                 "asm89/stack-cors": "^1.1",
@@ -597,6 +597,7 @@
                 "drupal/book": "self.version",
                 "drupal/breakpoint": "self.version",
                 "drupal/ckeditor": "self.version",
+                "drupal/ckeditor5": "self.version",
                 "drupal/claro": "self.version",
                 "drupal/classy": "self.version",
                 "drupal/color": "self.version",
diff --git a/core/core.libraries.yml b/core/core.libraries.yml
index e2b2c4d3d5..a8e554104b 100644
--- a/core/core.libraries.yml
+++ b/core/core.libraries.yml
@@ -49,6 +49,7 @@ ckeditor5.editorDecoupled:
     assets/vendor/ckeditor5/build/editor-decoupled.js: { preprocess: false, minified: true }
   dependencies:
     - core/ckeditor5
+    - core/ckeditor5.htmlSupport
 
 ckeditor5.internal:
   remote: *ckeditor5Remote
@@ -163,9 +164,6 @@ ckeditor5.language:
   remote: *ckeditor5Remote
   version: *ckeditor5Version
   license: *ckeditor5License
-  css:
-    component:
-      css/language.css: {}
   js:
     assets/vendor/ckeditor5/build/language.js: { preprocess: false, minified: true }
   dependencies:
diff --git a/core/modules/ckeditor5/ckeditor5.module b/core/modules/ckeditor5/ckeditor5.module
index 0ac517bc19..0d7b8bf82f 100644
--- a/core/modules/ckeditor5/ckeditor5.module
+++ b/core/modules/ckeditor5/ckeditor5.module
@@ -26,7 +26,7 @@ function ckeditor5_help($route_name, RouteMatchInterface $route_match) {
     case 'help.page.ckeditor5':
       $output = '';
       $output .= '<h3>' . t('About') . '</h3>';
-      $output .= '<p>' . t('The CKEditor 5 module provides the <a href=":cke_url">CKEditor 5 text editor</a> for WYSIWYG HTML editing in text fields. The CKEditor 5 module uses the framework provided by the <a href=":text_editor">Text Editor module</a>.', [':cke_url' => 'https://ckeditor.com/ckeditor-5/', ':text_editor' => Url::fromRoute('help.page', ['name' => 'editor'])->toString()]) . '</p>';
+      $output .= '<p>' . t('The CKEditor 5 module provides a highly-accessible, highly-usable visual text editor and adds a toolbar to text fields. Users can use buttons to format content and to create semantically correct and valid HTML. The CKEditor module uses the framework provided by the <a href=":text_editor">Text Editor module</a>. It requires JavaScript to be enabled in the browser. For more information, see the <a href=":doc_url">online documentation for the CKEditor 5 module</a> and the <a href=":cke5_url">CKEditor 5 website</a>.', [':doc_url' => 'https://www.drupal.org/docs/contributed-modules/ckeditor-5', ':cke5_url' => 'https://ckeditor.com/ckeditor-5/', ':text_editor' => Url::fromRoute('help.page', ['name' => 'editor'])->toString()]) . '</p>';
       $output .= '<h3>' . t('Uses') . '</h3>';
       $output .= '<dl>';
       $output .= '<dt>' . t('Enabling CKEditor 5 for individual text formats') . '</dt>';
@@ -364,6 +364,11 @@ function ckeditor5_validation_constraint_alter(array &$definitions) {
  * Implements hook_config_schema_info_alter().
  */
 function ckeditor5_config_schema_info_alter(&$definitions) {
+  // In \Drupal\Tests\config\Functional\ConfigImportAllTest, this hook may be
+  // called without ckeditor5.pair.schema.yml being active.
+  if (!isset($definitions['ckeditor5_valid_pair__format_and_editor'])) {
+    return;
+  }
   // @see filter.format.*.filters
   $definitions['ckeditor5_valid_pair__format_and_editor']['mapping']['filters'] = $definitions['filter.format.*']['mapping']['filters'];
   // @see @see editor.editor.*.image_upload
diff --git a/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5AllowedTagsTest.php b/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5AllowedTagsTest.php
index 0e189d074e..4e8a41b963 100644
--- a/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5AllowedTagsTest.php
+++ b/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5AllowedTagsTest.php
@@ -320,6 +320,11 @@ public function testAllowedTags() {
     $page->pressButton('Save configuration');
     $assert_session->pageTextContains('The text format ckeditor5 has been updated');
     $assert_session->pageTextNotContains('The following tag(s) are already supported by enabled plugins and should not be added to the Source Editing "Manually editable HTML tags" field: Bold (<strong>)');
+
+    // Ensure that CKEditor can be initialized with Source Editing.
+    // @see https://www.drupal.org/i/3231427
+    $this->drupalGet('node/add');
+    $this->assertNotEmpty($assert_session->waitForElement('css', '.ck-editor'));
   }
 
   /**
diff --git a/core/modules/ckeditor5/tests/src/Kernel/CKEditor5PluginManagerTest.php b/core/modules/ckeditor5/tests/src/Kernel/CKEditor5PluginManagerTest.php
index 1bca03aac4..88ffa0191c 100644
--- a/core/modules/ckeditor5/tests/src/Kernel/CKEditor5PluginManagerTest.php
+++ b/core/modules/ckeditor5/tests/src/Kernel/CKEditor5PluginManagerTest.php
@@ -333,10 +333,10 @@ public function testEnabledPlugins() {
     ];
     $this->assertSame($default_plugins, $definitions, 'No CKEditor 5 plugins found besides the built-in ones.');
     $default_libraries = [
-      'ckeditor5/ckeditor5.basic',
-      'ckeditor5/ckeditor5.internal',
       'ckeditor5/drupal.ckeditor5',
-      'ckeditor5/drupal.ckeditor5.emphasis',
+      'core/ckeditor5.basic',
+      'core/ckeditor5.internal',
+      'core/drupal.ckeditor5.emphasis',
     ];
     $this->assertSame($default_libraries, $this->manager->getEnabledLibraries($editor));
 
@@ -362,9 +362,9 @@ public function testEnabledPlugins() {
     // Sort on plugin id.
     asort($default_plugins_with_layercake);
     $this->assertSame(array_values($default_plugins_with_layercake), $plugin_ids);
-    $this->assertSame(array_merge($default_libraries, [
-      'ckeditor5_test/layercake',
-    ]), $this->manager->getEnabledLibraries($editor));
+    $default_libraries_with_layercake = array_merge($default_libraries, ['ckeditor5_test/layercake']);
+    sort($default_libraries_with_layercake);
+    $this->assertSame($default_libraries_with_layercake, $this->manager->getEnabledLibraries($editor));
 
     // Enable media embed filter which the CKEditor 5 media plugin requires.
     $editor->getFilterFormat()->setFilterConfig('media_embed', ['status' => TRUE])->save();
@@ -378,10 +378,12 @@ public function testEnabledPlugins() {
     ]);
     sort($expected_plugins);
     $this->assertSame($expected_plugins, $plugin_ids);
-    $this->assertSame(array_merge($default_libraries, [
+    $expected_libraries = array_merge($default_libraries, [
       'ckeditor5/drupal.ckeditor5.media',
       'ckeditor5_test/layercake',
-    ]), $this->manager->getEnabledLibraries($editor));
+    ]);
+    sort($expected_libraries);
+    $this->assertSame($expected_libraries, $this->manager->getEnabledLibraries($editor));
 
     // Case 5: GHS is only enabled for Full HTML (or any other text format that
     // has no TYPE_HTML_RESTRICTOR filters).
@@ -397,11 +399,11 @@ public function testEnabledPlugins() {
     ];
     $this->assertSame($default_plugins, $definitions, 'No CKEditor 5 plugins found besides the built-in ones.');
     $default_libraries = [
-      'ckeditor5/ckeditor5.basic',
-      'ckeditor5/ckeditor5.htmlSupport',
-      'ckeditor5/ckeditor5.internal',
       'ckeditor5/drupal.ckeditor5',
-      'ckeditor5/drupal.ckeditor5.emphasis',
+      'core/ckeditor5.basic',
+      'core/ckeditor5.htmlSupport',
+      'core/ckeditor5.internal',
+      'core/drupal.ckeditor5.emphasis',
     ];
     $this->assertSame($default_libraries, $this->manager->getEnabledLibraries($editor));
   }
diff --git a/core/modules/ckeditor5/tests/src/Kernel/StarterTemplateTest.php b/core/modules/ckeditor5/tests/src/Kernel/StarterTemplateTest.php
deleted file mode 100644
index 4f1edacaba..0000000000
--- a/core/modules/ckeditor5/tests/src/Kernel/StarterTemplateTest.php
+++ /dev/null
@@ -1,74 +0,0 @@
-<?php
-
-namespace Drupal\Tests\ckeditor5\Kernel;
-
-use Drupal\Component\Serialization\Json;
-use Drupal\KernelTests\KernelTestBase;
-
-/**
- * Tests to ensure the starter template files remain current.
- *
- * @group ckeditor5
- */
-class StarterTemplateTest extends KernelTestBase {
-
-  /**
-   * Confirm starter template files are current with module files.
-   *
-   * The starter template includes several copies of files used by the
-   * CKEditor 5 module for JavaScript plugin builds, but with slightly modified
-   * to make them more suitable for use in contrib. To ensure the two versions
-   * of these very similar (or identical) files remain in sync, this test
-   * monitors changes to them and ensures files that should be identical still
-   * are, and non-identical files should still receive equivalent changes.
-   */
-  public function testStarterTemplateFilesCurrent() {
-    $module_path = $this->container->get('extension.list.module')->getPath('ckeditor5');
-
-    $package_json_template = "$module_path/ckeditor5_plugin_starter_template/js/package.json";
-    $package_json = "$module_path/package.json";
-    $this->assertFileExists($package_json);
-    $this->assertFileExists($package_json_template);
-
-    // Ensure that crucial parts of the package.json files match.
-    $this->assertSame($this->getCrucialPackageJsonSubsets($package_json), $this->getCrucialPackageJsonSubsets($package_json_template));
-
-    $webpack_config = "$module_path/ckeditor5_plugin_starter_template/js/webpack.config.js";
-    $webpack_config_template = "$module_path/webpack.config.js";
-    $this->assertFileExists($webpack_config);
-    $this->assertFileExists($webpack_config_template);
-
-    $webpack_config_hash = md5_file($webpack_config);
-    $webpack_config_template_hash = md5_file($webpack_config_template);
-
-    $this->assertSame('551c9cb2dc1a3615d6c142c2c76067b3', $webpack_config_hash, "This test has detected changes in $webpack_config. Please see if any of the changes made in this file should also be made in $webpack_config_template, an equivalent version of this file provided to module developers. Once it's confirmed these two files are current with one another, change the first argument in this test to $webpack_config_hash so it will pass.");
-    $this->assertSame('b28c2ee0b82e3cd154be4c6e20252210', $webpack_config_template_hash, "This test has detected changes in $webpack_config_template. Please see if any of the changes made in this file should also be made in $webpack_config, the file this template is based on. Once it's confirmed these two files are current with one another, change the first argument in this test to $webpack_config_template_hash so it will pass.");
-
-    $manifest = "$module_path/js/drupal/scripts/manifest.js";
-    $manifest_template = "$module_path/ckeditor5_plugin_starter_template/js/scripts/manifest.js";
-    $this->assertFileExists($manifest);
-    $this->assertFileExists($manifest_template);
-
-    $manifest_hash = md5_file($manifest);
-    $manifest_template_hash = md5_file($manifest_template);
-
-    $this->assertSame('87964f6830ef1416c9da898659fc3adf', $manifest_hash, "This test has detected changes in $manifest. Please see if any of the changes made in this file should also be made in $manifest_template, an equivalent version of this file provided to module developers. Once it's confirmed these two files are current with one another, change the first argument in this test to $manifest_hash so it will pass.");
-    $this->assertSame('b83d7c7d1b882db654755020df7dfe6e', $manifest_template_hash, "This test has detected changes in $manifest_template. Please see if any of the changes made in this file should also be made in $manifest, the file this template is based on. Once it's confirmed these two files are current with one another, change the first argument in this test to $manifest_template_hash so it will pass.");
-  }
-
-  /**
-   * Get crucial package.json subsets.
-   *
-   * @param string $package_json_path
-   *   Path for a package.json file.
-   *
-   * @return array
-   *   An array that include crucial parts of the package.json.
-   */
-  protected static function getCrucialPackageJsonSubsets(string $package_json_path): array {
-    $safe_to_be_out_of_sync = ['name', 'version', 'description', 'author', 'license', 'scripts'];
-    $json = JSON::decode(file_get_contents($package_json_path));
-    return array_diff_key($json, array_flip($safe_to_be_out_of_sync));
-  }
-
-}
diff --git a/core/tests/Drupal/KernelTests/Core/Asset/ResolvedLibraryDefinitionsFilesMatchTest.php b/core/tests/Drupal/KernelTests/Core/Asset/ResolvedLibraryDefinitionsFilesMatchTest.php
index 32040acacc..bdab04e2e9 100644
--- a/core/tests/Drupal/KernelTests/Core/Asset/ResolvedLibraryDefinitionsFilesMatchTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Asset/ResolvedLibraryDefinitionsFilesMatchTest.php
@@ -74,6 +74,8 @@ class ResolvedLibraryDefinitionsFilesMatchTest extends KernelTestBase {
   protected $librariesToSkip = [
     // Locale has a "dummy" library that does not actually exist.
     'locale/translations',
+    // The "CKEditor 5 Dev tools" module has an external asset library.
+    'ckeditor5_dev/ckeditor5_dev',
   ];
 
   /**