Summary: Please manually delete /etc/profile.d/locale.sh before updating. If . /etc/rc.conf fails in your login shell, please read the full announcement.
Changes to locale handling:
/etc/profile.d/locale.sh is now a static file that sources the correct config files in order to set your locale, rather than being generated at boot. The benefit of this is one less write to /etc, and it allows changes to the locale to take effect without rebooting (just relogin).
We add support for /etc/locale.conf. The settings in this file takes precedence over /etc/rc.conf, and those who use shells that cannot source /etc/rc.conf are required to move to this new format. /etc/locale.conf contains a new-line separated list of variable assignments. The variables we support are LANG as well as the LC_* variables (with the exception of LC_ALL). The format is shared with systemd.