You can modify existing translation files or add new language files. But don’t put your files in the plugin directory wp-filebase-pro/languages, otherwise they will be deleted on next plugin update!
This is how you make your translation files surviving updates:
Add this line to your wp-config.php:
/* That's all, stop editing! Happy blogging. */
Then create the directory wp-content/wpfb-lang and put the .mo files in there. Mind the name pattern:
You can use template.po as a template for translation. Poedit is a nice gettext editor.