Facebook's development utilizes a combination of programming languages and technologies, primarily focusing on PHP for server-side code. While HTML and CSS serve as markup languages for structure and styling, JavaScript is employed for client-side interactions rather than robust application development. The platform also incorporates C++, Erlang, Python, and potentially other languages, but Java is not a primary component. Instagram shares a similar technological foundation, relying heavily on PHP and related technologies. For a comprehensive overview of the programming languages used at Facebook, a detailed source is available on Quora.