I obviously found the file responsible of displaying the contact form with
FireBug, changed the displayed names in the input area and then re-upload my file, however, nothing was changed.
The input value of the first area was
your name, i changed it to
votre nom, but still displying me
your name. You can check it in this url, you can use FireBug to check this. Here is a sceenshot, and I'm use the Boldy theme: