Henrik Danielsson
--- a/core/modules/ckeditor5/tests/src/Unit/CKEditor5Test.php
+++ b/core/modules/ckeditor5/tests/src/Unit/CKEditor5Test.php
+}
+
+namespace Drupal\ckeditor5\Hook;
+
+if (!function_exists('_ckeditor5_get_langcode_mapping')) {
+
+  /**
+   * Mock language mapping between Drupal and CKEditor 5.
+   *
+   * @param string|bool $lang
+   *   The Drupal langcode to match.
+   *
+   * @return array|mixed|string
+   *   The associated CKEditor 5 langcode.
+   */
+  function _ckeditor5_get_langcode_mapping($lang = FALSE) {
-  function _ckeditor5_get_langcode_mapping($lang = FALSE) {
+  function _ckeditor5_get_langcode_mapping(string|bool $lang = FALSE): array|mixed|string {
--- a/core/modules/ckeditor5/tests/src/Unit/CKEditor5Test.php
+++ b/core/modules/ckeditor5/tests/src/Unit/CKEditor5Test.php
+    $this->assertEquals($expected_javascript, $javascript);
+  }
+
+}
+
+namespace Drupal\ckeditor5\Hook;
+
+if (!function_exists('_ckeditor5_get_langcode_mapping')) {
+
+  /**
+   * Mock language mapping between Drupal and CKEditor 5.
+   *
+   * @param string|bool $lang
+   *   The Drupal langcode to match.
+   *
+   * @return array|mixed|string
--- a/core/modules/ckeditor5/tests/src/Unit/CKEditor5Test.php
+++ b/core/modules/ckeditor5/tests/src/Unit/CKEditor5Test.php
+    // There was no placeholder to get the weight from.
+    $expected_javascript['keep_this']['weight'] = 0;
+    $this->assertEquals($expected_javascript, $javascript);
+  }
+
+}
+
+namespace Drupal\ckeditor5\Hook;
+
+if (!function_exists('_ckeditor5_get_langcode_mapping')) {
+
+  /**
+   * Mock language mapping between Drupal and CKEditor 5.
+   *
+   * @param string|bool $lang
+   *   The Drupal langcode to match.
--- a/core/modules/ckeditor5/src/Hook/Ckeditor5Hooks.php
+++ b/core/modules/ckeditor5/src/Hook/Ckeditor5Hooks.php
+      foreach ($assets->getAlreadyLoadedLibraries() as $library) {
+        if (str_starts_with($library, 'core/ckeditor5.translations.')) {
+          $filter_scripts = TRUE;
+          break;
+        }
+      }
+    }
    // This file is used to get a weight that will make it possible to aggregate
    // all translation files in a single aggregate.
    $ckeditor_dll_file = 'core/assets/vendor/ckeditor5/ckeditor5-dll/ckeditor5-dll.js';
-    if (isset($javascript[$placeholder_file])) {
+    if ($filter_scripts) {
      // Use the placeholder file weight to set all the translations files
      // weights so they can be aggregated together as expected.
-      $default_weight = $javascript[$placeholder_file]['weight'];
+      $default_weight = $javascript[$placeholder_file]['weight'] ?? 0;