Wordpress Multi-language Content

Greetings,

I have a wordpress instalation for my team, with training content and information.
On this blog I will have content for diferent languages.

So, I want do add a dropdown menu, so people can choose that language, and the main menu would change accordingly to that choise.
Example: english =>menu-en, portuguese/brazil =>menu-pt,...

And I want this choice to be remember for the next time the user logs in again.

Can you give me some tips on how can I do this, please?

Thanks,
Diogo Gomes