cs1|2 templates validate the content of |language= against language codes and names supported by MediaWiki. This page lists the language codes and names that MediaWiki supports. Language name and code pairs marked with a super-scripted dagger (†) are codes / names that are overridden by codes / names defined in Module:Citation/CS1/Configuration. See §Overridden codes / names. Use of language codes / names not found in these lists will cause Module:Citation/CS1 to place the article in Category:CS1 maint: unrecognized language.
Nota bene: When evaluating the value assigned to |language=, Module:Citation/CS1 looks first in MediaWiki's list of language names before looking in the list of language tags. There are several languages that have tags that match the spelling of the language name: Fon (fon), Isu (isu), Luo (luo), tiv (tiv), vai (vai), Yao (yao). There are two where the language tag matches the spelling of another language's name:
ga– language tag for Irish matches spelling of Ga language (gaa)ho– language tag for Hiri Motu matches spelling of Ho language (hoc)
When citing Irish- and Hiri Motu-language sources, use |language=Irish and |language=Hiri Motu.