Language modifications not working properly

Hello

Does anyone know why no modifications to the .po file inside the wp-content/plugins/i18n/woocommerce-sl_SI.po seem to work.

I have downloaded a version of the slovenian translation from: https://github.com/maticer/WooCommerce-Slovenian

However it is not translated 100% so therefore I have to manually translate it however no changes seem to apply. I have changed the language inside the wp-config.php file because it does show most of the content in Slovenian language. But as I said no changes apply after I edit the .po file and reupload to the server.

Anyone knows how to fix it?
Thanks in advance!

http://wordpress.org/plugins/woocommerce/