Die aktuell aktiven Locales stehen in /var/lib/locales/supported.d/local, alle verfügbaren kann man unter /usr/share/i18n/SUPPORTED nachsehen.
Neu generieren kann man die Locales dann per
$ dpkg-reconfigure locales
On Ubuntu 8.10, the files are in /var/lib/locales/supported.d. The current locale is in the file local, all installed locales are in the directory de, en and so on.
To reconfigure the locales after modifying the files, run dpkg-reconfigure locales.