For ex.

I`m from Macedonia, and when I open Mozilla[dot]com I`m recognized, and the left green Download Firefox Free banner, it says 2.0.0.12 for Windows, Macedonian (5.7MB). I guess when someone from England opens the site, the banner says English (X.XMB).
I hope someone can give me a explanation on how to do this.
Thank You !

The most probably is its use some function to recognize the country through your IP. There is a database with pairs "IP From - IP To" - "Country". The function (or class) take the value of the Country from the database with the ip given as parameter.
Is not 100% correct, but work good.
There is several pay services to make this too. In some cases you get country and city.
It is a link to download a php function. You need the funcion and the database. Here is the instructions.
http://chir.ag/tech/download/geoiploc/
In PHPClasses there is several like this too.
This is a pay service that give more data than the country:
http://www.ip2location.com/free.asp

In google "ip to country" or "ip to location" appears several good results. I dont remember, but if you need, i can search in my other machine: i used a script that not use database, it use a text file to retrieve the information.
The problem with all of this scripts is that the information must be updated frequently.

Either IP or Accept-Language HTTP header

i was going to say that.

I would *think* in that kind of case the http header might be better because then its the users *chosen* lanaguage if you know what i mean.

Dan