He fet el següent tal i com m'ha semblat entendre:

ignasi <at> ignasi-desktop:~$ cat /etc/default/locale
LANG="ca_ES.UTF-8"
LANGUAGE="ca_ES:ca:en_GB:en"
ignasi <at> ignasi-desktop:~$ cat /etc/environment
PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games"
LANG="ca_ES.UTF-8"
LANGUAGE="ca_ES:ca:en_GB:en"
ignasi <at> ignasi-desktop:~$ cat /var/lib/locales/supported.d/local
ca_AD.UTF-8 ISO-8859-15
en_US.UTF-8 UTF-8
ignasi <at> ignasi-desktop:~$ sudo dpkg-reconfigure locales
Generating locales...
  ca_AD.ISO-8859-15... up-to-date
  ca_AD.ISO-8859-15... up-to-date
  ca_AD.UTF-8... up-to-date
  ca_ES.UTF-8... up-to-date
  ca_ES.UTF-8 <at> valencia... up-to-date
  ca_FR.UTF-8... up-to-date
  ca_IT.UTF-8... up-to-date
  en_AU.UTF-8... up-to-date
  en_BW.UTF-8... up-to-date
  en_CA.UTF-8... up-to-date
  en_DK.UTF-8... up-to-date
  en_GB.UTF-8... up-to-date
  en_HK.UTF-8... up-to-date
  en_IE.UTF-8... up-to-date
  en_IN.UTF-8... up-to-date
  en_NZ.UTF-8... up-to-date
  en_PH.UTF-8... up-to-date
  en_SG.UTF-8... up-to-date
  en_US.UTF-8... up-to-date
  en_ZA.UTF-8... up-to-date
  en_ZW.UTF-8... up-to-date
  es_AR.UTF-8... up-to-date
  es_BO.UTF-8... up-to-date
  es_CL.UTF-8... up-to-date
  es_CO.UTF-8... up-to-date
  es_CR.UTF-8... up-to-date
  es_DO.UTF-8... up-to-date
  es_EC.UTF-8... up-to-date
  es_ES.UTF-8... up-to-date
  es_GT.UTF-8... up-to-date
  es_HN.UTF-8... up-to-date
  es_MX.UTF-8... up-to-date
  es_NI.UTF-8... up-to-date
  es_PA.UTF-8... up-to-date
  es_PE.UTF-8... up-to-date
  es_PR.UTF-8... up-to-date
  es_PY.UTF-8... up-to-date
  es_SV.UTF-8... up-to-date
  es_US.UTF-8... up-to-date
  es_UY.UTF-8... up-to-date
  es_VE.UTF-8... up-to-date
Generation complete.
ignasi <at> ignasi-desktop:~$ griffith
Traceback (most recent call last):
  File "/usr/bin/griffith", line 1139, in <module>
    griffith = Griffith()
  File "/usr/bin/griffith", line 73, in __init__
    initialize.locations(self)
  File "/usr/share/griffith/lib/initialize.py", line 42, in locations
    defaultLang, defaultEnc = getdefaultlocale()
  File "/usr/lib/python2.5/locale.py", line 443, in getdefaultlocale
    return _parse_localename(localename)
  File "/usr/lib/python2.5/locale.py", line 375, in _parse_localename
    raise ValueError, 'unknown locale: %s' % localename
ValueError: unknown locale: ca_AD

Segueix sense funcionar, però no sé si m'has donat una instrucció o he de modificar alguns arxius a mà

Gràcies
--
Ignasi Jarauta Rovira