Languages and variants can be rendered via the data-portlets object (Manual:SkinMustache.php#DataPortletsObject).
If you need to be able to test this locally on a wiki without languages you can use Extension:MobileFrontendContentProvider or skins.wmflabs.org.
I was following the skinlabs starter skin and found the following line in the ContentHeading.mustache file. can you please tell me what it does and how it works?
<a href="#lang" class="mw-interlanguage-selector mw-ui-button content__language-btn">{{msg-otherlanguages}}</a>
I added a interwiki language and added the language in the article. But that showed up below the main content via Languages.mustache. I also want to about the variants
https://m.mediawiki.org/wiki/Manual:How_to_make_a_MediaWiki_skin#Rendering_template_partials
With languages the example assumes it will be progressively enhanced by the Extension:UniversalLanguageSelector due to the prescence of the class mw-interlanguage-selector
