How to use translations

[Detvanec]

Hi!
How shoudl I use translation? I createt folder sk_SK in i18n folder. I created main.php with slovak translation there and set up language parameter to sk_SK. I recieved this error:

Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at /home/brejovci/public_html/mato/CHAT/phpfreechat-1.2/i18n/sk_SK/main.php:1) in /home/brejovci/public_html/mato/CHAT/phpfreechat-1.2/src/pfcuserconfig.class.php on line 25