I\'m researching hours and hours, but I could not find any clear, efficient way to make it :/
I have a codeigniter base website in English and I have to add a Polish
When managing the actual files, things can get out of sync pretty easily unless you're really vigilant. So we've launched a (beta) free service called String which allows you to keep track of your language files easily, and collaborate with translators.
You can either import existing language files (in PHP array, PHP Define, ini, po or .strings formats) or create your own sections from scratch and add content directly through the system.
String is totally free so please check it out and tell us what you think.
It's actually built on Codeigniter too! Check out the beta at http://mygengo.com/string