in which language is facebook designed?

[Rahul]

is it PHP?

[brisray]

PHP

Take a look at the filenames

http://www.facebook.com/login.php
http://apps.facebook.com/wildones/index.php
http://www.facebook.com/campaign/landing.php
http://touch.facebook.com/home.php

[TAG]

parsi

[vinoth]

Facebook uses PHP programming language

[Moe]

Its English

[rax]

It uses mixing language content.
Most of the scripts are written in their own markup language FBML(FACE BOOK MARKUP LANGUAGE)
It's a great thing to learn , if you're interested, and If you want to learn more a about it, then Search on facebook for Facebook Engineering..... And also visit developers.facebook.com if you want to learn and make your own facebook applications.

[Harsimran Singh]

http://www.webmasterindia.com/facebook_design.htm
Open the link above.