I have also a setup like this in the model:

public function resolveRouteBinding($slug, $field = null)
    {
        $page = app(PageRepository::class)->forNestedSlug($slug);

        abort_if(! $page, 404);

        return $page;
    }

    // #region routekey
    public function getLocalizedRouteKey($locale)
    {
        return $this->getNestedSlug($locale);
    }

And combining that with whats told on https://twill.io/docs/3.x/crud-modules/nested-modules.html#self-nested-modules here, but i cant make it work 😮