Which language is good for build a social networking site?

Answer 1

Well, nearly any language can work.
Facebook for example is written heavily in a special type of PHP, D and C++

For your situation you can probably do it with some html, css, js then how you do the back-end is up to you.

Answer 2

PHP, HTML, CSS, JS

PHP for Server side code (instead maybe Ruby, Node.js),
HTML for Presentation,
CSS for Styling,
JS for Client side