On Ubuntu, to add a locale to the system, I would edit /var/lib/locales/supported.d/local, add the locale and then run dpkg-reconfigure locales.
I tried that on a Debian 5.0, but I discovered that locales wasn't installed, but instead I had belocs-locales-bin and belocs-locale-data. There was also a locales package, not installed, that, when I tried to install was in conflict with belocs, so I refrained.
I found out that to reconfigure locales, I had to edit /etc/locale.gen and run locale.gen.
I was wondering what's the difference between the two systems, and why there are two systems?
