The language icon (文A) appears in Wikidata and Mediawiki on mobile web (such as https://m.wikidata.org/ and https://m.mediawiki.org/ ; the mobile view uses the Minerva skin), but doesn't do anything useful.
It could do useful things, for example switch the language is UI, labels, etc., or to move to the article in the projects according to sitelinks.
Since it is unusable, it should be disabled for the time being
- Update mediawiki-config so that MinervaAlwaysShowLanguageButton defaults to true for all wikis except mediawikiwiki and wikidatawiki where it should be false
- Once you have been given the green light, schedule deployment of the change. Be sure to read up on https://wikitech.wikimedia.org/wiki/X-Wikimedia-Debug beforehand to check how you can test your change during that deploy window. @Jdlrobson can assist!