You may have heard that "compact language links" are expanding across
the wikis these days:*
https://www.mediawiki.org/wiki/Universal_Language_Selector/Compact_Language…
A crucial piece of this system is data on which languages are most
spoken in each country:
https://www.mediawiki.org/wiki/ULS/FAQ#language-territory
Please look at the CLDR data for the countries you know best; if you see
something clearly wrong or missing, please follow the "bug" link to
report it, and mention some official source.
Nemo
(*) Since at least 2010 there was a feature request to make the users
see more relevant list of interwiki links/interlanguage links on each
article. It takes up to 30 days for all articles on a wiki to be updated
to the new display, as the cache slowly expires for unregistered users.