AFAIK they use 'Hack', a language designed to be very similar to PHP. https://hacklang.org/ https://hacklang.org/ PHP is a lot better than it used to be now t

AFAIK they use 'Hack', a language designed to be very similar to PHP. https://hacklang.org/ https://hacklang.org/ PHP is a lot better than it used to be now though! It's got a bad rep but newer versions are fast and surprisingly modern-feeling.