When a user chooses a language of the article on the left panel, often the available languages are grouped according to their distribution on the continents. When I choose Oceania, the Spanish language is absent on the list, however it is also spoken on the Easter Island, which is indeed part of Oceania.
How to fix this (for developers):
This must first be done in the https://github.com/wikimedia/language-data repository. Only after it's merged there in GitHub, it must be updated in Wikimedia Gerrit in the mediawiki/extensions/UniversalLanguageSelector repository in the lib/jquery.uls/src/jquery.uls.data.js file.