In https://gerrit.wikimedia.org/r/#/c/28238 $wgExtraLanguageNames values were added for WikiVoyage.
This $wgExtraLanguageNames global is for languages. Its values are used in various language-related functions, that expect actual languages. Feeding these functions anything else will break things.
The values here look like they are supposed to be served by interwiki prefixes (not interlanguage).
Version: wmf-deployment
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=68815