Words in data.php doesn't change with po file

Hi,
I use directory plugin and translate it with po editor almost all the words changed but words that are in the : /public_html/wp-content/plugins/directory/core/data.php
are not change (all the listing words). The other words in other files change so I think it something on that file that not work. Just to clear it the words from that file are found on the po file but after I translate them they are not change on the website. (like others words from other files) Thanks