I think many language. to begin with XHTML/CSS. I think also Python, because there is some page with .py as extension. Do you want to make a Google Like ?
Python with xhtml, css and mysql / php with robust databses serving content from across the globe based upon the search with the serps created based upon input and the closest server's results. There is a huge database backend, mysql is too weak, same as posgresql -- It would my SQL or Oracle but the database has to be very powerful on the backend for speed and flex when it comes to serps creation and deployment to searcher