Currently, it's not possible to add localization to a sitemap.xml in a multilingual site accordingly to the Google recommendations
https://support.google.com/webmasters/answer/189077
The possibility to generate sitemaps like this:
```
<url>
<loc>http://www.example.com/english/page.html</loc>
<xhtml:link
rel="alternate"
hreflang="de"
href="http://www.example.com/deutsch/page.html"/>
<xhtml:link
rel="alternate"
hreflang="de-ch"
href="http://www.example.com/schweiz-deutsch/page.html"/>
<xhtml:link
rel="alternate"
hreflang="en"
href="http://www.example.com/english/page.html"/>
</url>
I just noticed that this package depends on https://github.com/ekalinin/sitemap.js#example-of-indicating-alternate-language-pages, so it's actually possible to add alternate URLs
In case someone wondering we just define the route as:
` { url: 'nosotros', changefreq: 'monthly', priority: 0.9, lastmodISO: moment().format(), links: [ { lang: 'en', url: 'en/about-us' } ] },