The handbook used to tell people to copy a file from /usr/share/timezone into /etc/localtime (it really should have been a symlink for timezone updates to fix things) so that `date` would be properly localized. Coincidentally, KDE relies on this for the default system timezone as well. At some point, this was removed. I caught it when doing a new install. It should be added again.
It is part of the first steps in the chroot, https://wiki.gentoo.org/wiki/Handbook:AMD64/Installation/Base The file is generated as part of the timezone-data package configuration.
My mistake. Thanks.