best way to create multilingual website

Hi
I've never created a multi lingual website from scratch and wondered what the most effective, easiest to update way is. I know you can literally hand translate and have separate site for each language but I cannot imagine that's the best way. Is there a php mod, javascript, etc. that will literally output the correct language based on user selection? I use a shopping cart mod called osCommerce and have one setup at incamaine dot com which gives 3 languages. Maybe I could "tear that apart" and see what makes it tick. Any thoughts??