I'm in the works of creating a social networking concepts. I have run into a few questions along the way however:
1. What is Facebook's ad platform, and how did they make it?
2. How does Facebook know your location and more so, provide you with relevant ads?
3. How does creating a login/signup page work?
4. How does Facebook make money?
2. I dont know exactly how facebook knows where you live, but most likely it's the computer IP-adress and maybe the sign-up location.
3. Depends on what language you choose, and it's a long explanation. To make it short you assign variables to text-fields, when the user submits the form the script gets the values inside the text-fields and saves it in a database.
On top of that there might be some validations, and maybe a confirmation email.
Google "login form tutorial" for more info.
4. The most obvious way they make money is with ads. And recently they started testing their facebook credits for games.
Also, it seems to me that if you're interested in creating a social networking system, basing your model on "what Facebook does" is probably a failing venture. They already did it, and they have much more money and manpower than you ever will, and they will always win that particular game.
Same goes for Twitter, LinkedIn, FourSquare, and pretty much every other dominant social site you can name.
If you want a chance at success, don't play the game. Someone else has already beat you. Change the rules and do something unique and different. This is your only chance at having any significant following in today's Internet, and if you do that part right, you won't need to care about "what Facebook does."
Languages are translated using a standard called i18n which requires Unicode compliance. Most web frameworks like Django provide support for the most common languages and I am sure you can find numerous more to add in.