How http://www.debian.org handles languages

[Spencer Wilson <spencer.wilson@comcast.net>]

Hello,

I'm not sure if this is appropriate to ask, but I thought that I should 
at least give it a try.

How does http://www.debian.org handle languages?

I noticed that a person or group of people made a translation of /x/ 
document. An example would be:
English, United States (index):
    index.en-us.htm

Swedish (index)
    index.sv.htm

My question is: How does http://www.debian.org know which file to use 
(based on the language settings of the users browser)?