Add language en_US Solaris 10

Hello,
I have a Sun Solaris 10 installs by default in French.
I do not have CDs of the OS installation.
I have a program use the language en_US.

At connection language chosen is C (en_USxxxx not available)
I open a console $ LANG C
if LANG = en_US I get "could not set correctly local"

Sun Microsystems Inc.. SunOS 5.10 Generic January 2005
# Echo $ LANG
C
# Sh
# LANG = en_US
Local could not set correctly

I think
edit /etc/default/init
TZ=Europe/Paris
CMASK=022
LC_COLLATE=fr_FR.ISO8859-1
LC_CTYPE=fr_FR.ISO8859-1
LC_MESSAGES=fr
LC_MONETARY=fr_FR.ISO8859-1
LC_NUMERIC=fr_FR.ISO8859-1
LC_TIME=fr_FR.ISO8859-1

remove all LC_*
and install the package LANG en.US UTF-8

I forget something?
But what package?

Thank you

read the manpage of "localeadm". you should find all you need there...

# localeadm -l
.....
The following regions are installed on ... on Fri Sep 11 14:10:19 CEST 2009
POSIX (C)
Western Europe (weu)
[France, Holland, Belgium (French), Belgium (Flemish), Ireland, England, Luxembourg (French), Luxembourg (German) ]

but where to find the package US.UTF-8 for used
localeadm -a en_US.UTF-8 -d /tmp/....