change language in URL

Cant find latest info on this.. but what URL do I use to change language:

http://5thupperstreet.com/index.php?language=en
http://5thupperstreet.com/index.php?lang=en
http://5thupperstreet.com/?lang=en

like that?

nothing of this works... and where can I find a simple code for listing all available languages? The normal drop-down for example..?