Comment 17 for bug 675014

For mod_fastcgi you'd probably have to use the following config line:
FastCgiConfig -initial-env LANG=fr_FR.utf8
This line without the equals sign and everything that follows it might already be enough, but the above is more likely to work.
See also http://www.fastcgi.com/drupal/node/25#FastCgiConfig
Perhaps I should include this pointer in the documentation.