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.