You can learn from http://www.solostream.com/blog/tutorials/translate-wordpress-theme/ about translating your site into your language. Pls make sure you add the entry for your language into wp-config.php file like this –
define ('WPLANG', 'fr_FR');
Pls use the pot files in ‘fitpro/languages’ folder as a template to create .po files.http://www.poedit.net/ -Poedit is the popular free editor for creating .po and the corresponding binary .mo files.
If you want to change it to an alternate string in English then you can change directly in file en_US.po (default one), just need to change the string and hit update button.
You may need to do an update in POEdit to see all the strings