Change the language in the theme

Hello!
I have just succeeded changing language to Swedish via the wp-config.php folder, im trying now to change the theme language and it is not working for me. Im using the theme twenty eleven and i’ve copied the .mo .po files to /wp-conten/themes/twentyeleven/languages and it’s still not working. So is it anything in my php i need to change please let me know as soon as possible! Many thanks!