The internet does not have a lingua franca. The web does, and it is HTML.

Sorry, that's total nonsense. Far more of the Internet depends on C, C++, or some mix of the two. Software written in them runs the networking gear, the servers, and the clients that are critical to the Internet's existence.

And keep in mind that the major JavaScript implementations today are all built using C and/or C++ in one way or another. So pretty much anywhere that JavaScript is being used, then C and C++ are being used, too.

JS is the lingua franca of the browser, but PHP is the lingua franca of the server side.