How are multiple signals propagated in a coaxial cable?
the RF signals of each frequency are translated into voltage waves that are then superimposed onto one, thereby creating one electrical signal that is sent through the cable.


On the one hand, I think you've got it. On the other, I'm not sure you understand what's going on well enough to get it for the right reasons.

If we want to broadcast an rf signal through space, we have to emit that signal from an antenna. To get the signal from our generating equipment to the antenna we use a transmission line, typically a coaxial cable. The voltage signal on the transmission line excites the antenna, which generates EM waves that travel to the receiving antenna.

At the receiving antenna, the EM waves are delivered to another transmission line (again, typically coax) to get them to the receiving equipment.

Sending signals over coax is just like that, but without the antennas. The generating equipment is just connected to the receiving equipment by the cable. The same voltage signals in the cable that would have excited the antenna, travelled through space, been collected by the other antenna, etc, are just delivered straight to the coax that feeds the receiving equipment.

My point is there's no fundamental difference between the signals in a coax cable and "rf signals". Both are just voltages (or electric fields) varying with time. 

And there's no need to "translate" rf signals into voltages. The RF signals already are (or started out as) voltages before they were broadcast as EM waves.

In fact you can also look at the signal in the coaxial cable as an EM wave, but it just happens to be travelling in a dielectric sandwiched between two conductors instead of travelling in free space.