And if you have your blog set to french, you can just do these steps in the loop:
// FIRST, SET THE WAY YOU WANT TO FORMAT DATE
// DETAILS HERE - http://php.net/manual/en/function.date.php
$dateformatstring = "l d F, Y";
// THEN, CONVERT THE FIELD FROM ACF TO UNIX TIMESTAMP
$unixtimestamp = strtotime(get_field('data_picker'));
// NOW ECHO THE FRENCH DATE USING A WORDPRESS FUNCTION
echo date_i18n($dateformatstring, $unixtimestamp);