Most general Zen Cart language text is held in files for versions up to and including Zen Cart 1.5. So installing the language packs for those languages will deal with a lot of your needs for French and Italian. But not all of it.
Category and Product information is held in the database and installing a language pack will not automatically translate that to a different language, you will need to arrange that yourself.
Zen Cart also allows you to insert blocks of HTML (through the define_pages editor) such as on the home page, or explanatory text on the shopping cart page. If you have used text in these HTML blocks, then you will need to translate that too.
A major exception on many sites would be pages created using Zen Cart's built in CMS, EZ-Pages. If you've done this, you will need to install the Multilingual EZ-Pages add-in module and then translate the pages created this way.
One final, and rare exception, would be if you have created any HTML banners. Most people don't so if you're not sure what this means, it probably doesn't affect you.