Man pages matching name locale::codes::langext in section 3pm:

Locale::Codes::LangExt.3pm.en	debian 10 / liblocale-codes-perl
Locale::Codes::LangExt.3pm.en	debian 11 / liblocale-codes-perl
Locale::Codes::LangExt.3pm.en	debian 12 / liblocale-codes-perl