Hi Zini , really a nice question, let me tell you what i know which technology Facebook using, As Facebook is a social utility that connects people around the web.
Server side scripting languages used by Facebook
mostly Facebook is using PHP that is popular scripting language for creating web pages, you can say 76 % of the site developed using PHP and then java ,and many others like python these language are used as server side scripting language by Facebook
Client side Programming Language used by Facebook
mostly they are using Java script for client side programming language
Markup languages used by Facebook
Facebook is using XHTML as their Markup language
Character Encoding used by Facebook
UTF-8(Eight bit Unicode Transformation Format) is a variable length character Unicoding which is backward compatible with ASCII.
Then they are using a vast number of Content languages like German,Japanese..
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