The suggestions in the ArchLinux link didn't work. However, I read a bit and flailed about and I *think* I may have solved it.
The problem with this is that it will force *everything* to comply with GB/UK settings. If you run 'locale' you'll see things like money, paper sizes, etc. are all changed and something would eventually bite back in some other app.
Additionally, some things I've read indicate that the GB time/day definitions are actually *wrong* because UK calendars mostly should start with Monday as the first weekday. The 'wrongness' just makes it correct for the US.
I found (what I think is) a better way.
The file /etc/profile.d/lang.sh sets the slackware default locale to en_US. I added a line under the existing export statement to make it read:
This changes only the TIME definitions to the (wrong?) GB values without messing with any of the other locale values.
At least it fixed orage.
I've read enough conflicting stuff on this that it makes my head asplode.
I *think* the text locale values in /usr/share/i18n/ get compiled into binary files that end up in /usr/lib/locale entries. That's why editing /usr/share/i18n/ entries don't work (at least not for me). It also appears to be a rather arcane process to compile the binary *and* apparently X uses some similar yet different locale scheme.
Hopefully this mess will get sorted out by those that actually know what's stored where and what the proper values should be. When that happens, removing the LC_TIME=en_GB entry above would be necessary.