Feature summary (what you would like to be able to do and where):

Somewhere in the wikimedia messages setup (allmessages) it would be helpful to have a mediawiki: type label for the sister wikis in each language. If that exists I cannot see it in the existing all messages, and obviously know where to find it and use it.

I see many examples of WMF wikis using mediawiki:sidebar and hardcording the respective wikilinks

An example
https://ta.wikinews.org/w/index.php?title=Mediawiki:Sidebar&oldid=53879

We already have Mediawiki:Wikimedia-sitematrix which can be utilised to head up that sort of section

So I am thinking of simple things,

Mediawiki:Wikidata-label or Mediawiki:Wikidata or Mediawiki:Wikimedia-Wikidata
Mediawiki:Wikisource-label or Mediawiki:Wikisource Mediawiki:Wikimedia-Wikisource
etc.

for each of the sisters: Wikivoyage, Wikidata, Wikiquote, WikiCommons, Wikipedia, Wikinews, Wiktionary, Wikibooks, Wikiversity, Meta, Wikisource

I don't know whether we need to go to the necessity of setting up the underlying links as standard wikimedia-messages as they are all set within Special:Interwiki though the technical minds may have a better understanding. For me it is the names and language translations as standard

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):

Mediawiki:Sidebar across all WMF wikis

Benefits (why should this be implemented?):

WMF wikis can quickly load up their wikisisters, and it will appear in the language of the visitor to better understand the link target. Very useful at wikis where default language is English.

Translations would be managed at translation wiki.

Note I am unaware of whether wikis can detect the language set by user in preference and have it active into a wikilink, eg. set w:{userlanguage}:linktarget