Facebook uses several different languages for its different services. PHP is used for the front-end, Erlang is used for Chat, Java and C++ are also used in several places (and perhaps other languages as well).
What language is Instagram written in?
Instagram, the world’s biggest online photo-sharing app, uses Python on its backend. According to Instagram’s engineering team, Instagram currently features the world’s largest deployment of the Django web framework, which is written entirely in Python.
What language is Google written in?