Filter alternate language links on a sitemap

I’m using @pedroborges sitemap plugin on a multilanguage site.

The blog only exists in the default language, and I would like to filter all the alternate language links for blog and its children pages.

I tried this, but it doesn’t work:

c::set('sitemap.process', function($pages) {
    return $pages->filter(function($page) {
        return $page->content(site()->language()->code())->exists();
    });
});

Any help?

I found a solution for the moment. I removed the plugin and I made the sitemap manually following the google content guidelines.

I know is not the most practical solution, specially if you have a lot of pages or many changes, but it allows you a complete control of the output.