There doesn't seem to be a libreoffice i18n language pack for UK (GB) English in the libreoffice multi-package. Looking at the Makefile, adding one is just a matter of adding "gb" to the languages array.
I tried to test this by building the port, but my machine lacks the necessary disk space and power. Could the gb language pack be added to the standard build please? There are probably enough potential users to make this worthwhile Chris Billington