gnome-terminal, azerty keyboard, accents problem

Hi,
I am connected to my linux centos 5.5 station with an azerty keyboard pc105, with some accentuated vowels available by pressing one button (no shift, no AltGr, etc.), such as:
éèçàù
I see them correctly on my screen just now and I hope that you can see them, too.
If you don't: I typed "e" with acute accent, then "e" with grave accent, then "c" with cedilla, then "a" with grave accent, then "u" with a grave accent.
I see them also when using firefox and OpenOffice, but neither at the shell level with gnome-terminal 2.16.0 nor with vim 7.0.
The same symptoms appear with the other accentuated vowels reached via pressing two buttons (e.g. to put a circonflex accent on the "a" or else).
The result of the locale command is:
LANG=en_US.UTF-8
LC_CTYPE="C"
LC_NUMERIC="C"
LC_TIME="C"
LC_COLLATE="C"
LC_MONETARY="C"
LC_MESSAGES="C"
LC_PAPER="C"
LC_NAME="C"
LC_ADDRESS="C"
LC_TELEPHONE="C"
LC_MEASUREMENT="C"
LC_IDENTIFICATION="C"
LC_ALL=C
What should I do to see the accentuated vowels when I type them within a line shell command or when inputting text with vim ?
I read a huge of web pages about that, but nothing works.
Once some pertinent change will be found, should I just reopen a new terminal window, or logout then login, or reboot ?
Thanks for any help.
Michel.

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