Mixfolio Theme translation

Hi,

I’m using Mixfolio theme :
https://graphpaperpress.com/themes/mixfolio/

And I’ve found a FRENCH translation here :
https://www.wptrads.com/theme/mixfolio/

The problem is: I don’t know what to do with the PO and MO files

I’ve been searching around and can’t find anything

My WPCONFIG is correctly configured with
define ('WPLANG', 'fr_FR');

I tried placing the PO and MO files in the theme root directory, and also in /wp-content/languages/

Please help!