Q & A FR translation not working --> polylang conflict ?

Hi,

I put qa-wordpress-questions-and-answers-plugin-fr_FR.po and qa-wordpress-questions-and-answers-plugin-fr_FR.mo in the languages folder of the qa plugin.

In wp-config.php, I added this one:
define('WPLANG', 'fr_FR');

But https://www.iraiser.eu/questions/ask/ is just staying in english. What could I do? Thanks !!

By the way, I'm using Polylang to have the website content in French and English, and this plugin works well.