table in Module:Language/data
connects Wikipedia language codes to the corresponding code used on the English Wiktionary. wikt:Wiktionary:Language treatment
records this relationship for ISO codes. For instance, all of bs
(Kajkavian) are placed under the header for sh
(Serbo-Croatian) in Wiktionary entries. See for instance wikt:kaj#Serbo-Croatian
, the word that Kajkavian is named after. The subsumed codes should still be used in language-tagging on Wikipedia.