Translation files doesn’t seem to work on WordPress MU

Hi,

I am trying to use translation files on a WordPress multisite environment. I followed the instructions given here: https://contactform7.com/contact-form-in-your-language/.

I switch the language here :
here : Users > Your Profile, fr_CA
here : Settings > General : fr_C
and even try to explicitly define the language in the wp-config.php ->(‘WPLANG’, ‘fr_CA’);

I made sure to copy the most recent language files (.PO and .MO) here:
/wp-content/plugins/contact-form-7/languages/contact-form-7-fr_CA.po

But the language still remains in English.

Have others encountered this problem?

Thanks!