LANG in /etc/environment and in .bashrc

[Robin Gerard <robin.jag@free.fr>]

Hello,
I would like to understand why, when I set LANG to C, in /etc/environment
and LANG to fr_FR.ISO-8859-1 in my .bashrc, after the login, I can't write
te letters with accents.
( However if I launch mutt, for example, the messages send by mutt are in 
French. )
On the other hand, if I run "bash" in command line, I can write the letters 
with accents. (But two "bash" are running) 
Is it possible that I can write the letters with accents after the login
with LANG=C in /etc/environment and export LANG=fr_FR.ISO-8859-1 in my
.bashrc ?
And how to do that ?

TIA
-- 
Gerard