Best practice for multi-language App

I'm designing the mockup of u web application and I found this product very usefull and practice. I bought the "lifetime" license. I need to prepare the mockup in differente languages: EN, SP and IT. Which is the best approach to follow?

Thanks for any help provided

No One? :-(

I usually have something to offer in here, but ... I don't ever work with multi language stuff on any of my sites so far so I don't have any advice to offer Vincenzo, sorry. Hopefully someone that has worked with it will chime in at some point.

Thanks for the answer anyway!

My Idea is to add a javascript able to choose the localized string from a resource file passing the StringID ...

I Tried to: 1) create a new javascript file with the following content: var lang = {}; lang["en"] = { hello_world: "Hello, World!", }; lang["es"] = { hello_world: "Hola Mundo!", };

2) I defined a new "Custom code" item with the following code: <script>lang["es"].hello_world;</script>

3) I added this Custom Code in my page but nothing appears!!!

Any clue or tips?