User's Language Preferences reverting to 'en' after sync

[trevormccready]

User's preferred langauges were all set to 'en_us' or 'en_us_wp' (on workplace site) and after a subsequent sync, their preferred languages were changed to 'en'. This appears to be coded in https://github.com/microsoft/o365-moodle/blob/master/local/o365/classes/feature/usersync/main.php to strip languages with longer than 2 characters. Is there a reason why langauge preference won't allow sub-language packs like en_us to be used?