Problem/Motivation
Sibling of #3228464: [upstream] API for contrib projects to load CKEditor translations.
See https://git.drupalcode.org/project/ckeditor5/-/merge_requests/56#note_39145.
This will need tests similar to \Drupal\Tests\ckeditor\Kernel\CKEditorTest::testJSTranslation()
for CKEditor 4 in core.