From: https://metacpan.org/release/DROLSKY/DateTime-Locale-1.33/source/Changes - Rebuilt all locale data with the data from CLDR 40.0.0. There are some notable data changes in CLDR 40.0.0. - Data change: The root locale is now named "und", not "root". - Data change: The "en-US-POSIX" locale has been removed from CLDR. If you load this locale you will now get the "en-US" locale.