Code snippet that can be used to to change contents Lang Direction in CKeditor drupal 8.
/**
* Implements hook_editor_js_settings_alter
*/
function MYMODULE_editor_js_settings_alter(array &$settings) {
foreach ($settings['editor']['formats'] as $name => $value) {
$settings['editor']['formats'][$name]['editorSettings']['contentsLangDirection'] = 'rtl';
}
}
