Broken redirect in multilingual environment

I'm having a similar issue: every time a form is restored, the action attribute of the form element gets changed to /en/en/node/nid/edit or /en/fr/node/nid/edit

I found the cause to be in function autosave_restore()

    // Because the form will by default submit back to this URL, we need to
    // tell it to actually submit back to where it would have submitted to
    // originally.
    $form['#action'] = **url**($record->path);

$record->path already contains the language prefix and the url function is adding another. A quick fix is to just output "/{$record->path}" but that will break some sites with an url prefix... I'm not sure if the fix should be worked here or earlier in the process...

OK there were 2 approaches to this: either we do not save language information with the form in autosave_form_alter(), i.e. replace $request_path = request_path(); with $request_path = drupal_get_path_alias();. This approach will remove any language info from the form. Since there does not seem to be a way to get the current language upon restoring (ajax call? the $language_url global is empty and $language always reverts to default), the restored form will always point to the site's default language upon saving.

Another approach is to leave the language in the autosaved form as it is now, and change the way the form action attribute is rebuilt in autosave_restore, as suggested in my first post. This would be done by changing the call to url(), ie

$form['#action'] = base_path().$record->path;

This allows to keep the original form language. Attached is a patch that implements this second approach.

See https://www.drupal.org/project/autosave/issues/2944324 for a fix with ajax calls and language and apply both patches