what kind site you are building?
very good chance there will be free systems close to what you want already, and many of these free systems come with multi-languages packages already.
such as forum systems, or shopping carts, the top rated free open source code systems are all with multi-language packages.
You can find a free open source codes systems and either install / modify for your usage or read their codes and learn from them and build up your own systems.
basically you will do like this in database, for example, for the e-shop products
you may have two tables, 1 called products, 1 called products_description.
table products holds these universal values,
products_id, price, product_code
table products_description holds these language specific values
products_id, language_id, product_name, product_description.
It is not so easy but it is not that difficult either. If you find a good open source code system you can learn a lot from it. Or maybe you can directly use it.
