how to set locale to French language on mail server ?

[Frank Bonnet]

Hello

I am a bit confuse on how to set "locale" to French language on our mail 
server , all our users user French keymap and actually the server
is NOT well configured

mail# locale
LANG=
LC_CTYPE="C"
LC_COLLATE="C"
LC_TIME="C"
LC_NUMERIC="C"
LC_MONETARY="C"
LC_MESSAGES="C"
LC_ALL=

I want to configure at server level for all users which file do I have
to setup FR as locale ?

I've the doc but it is a bit unclear to me ...

Thanks a lot.