If you have the time to look carefully at a boiling kettle, you can observe something interesting: When the water boils steam leaves the kettle through the spout and quickly condenses into water vapor after a couple of centimetres. Steam is invisible (I ignore the thermal distorsion here), vapor looks like a cloud. A phase-transition is going on here: steam is water dissolved in air, vapor is the same water condensed into tiny droplets. This condensation is thermo-dynamically determined by several factors like temperature, atmospheric pressure and humidity. The precise formula is not relevant now, you can just see what happens by watching.
I mention this because neither German nor Spanish distinguish to the best of my knowledge between steam and vapor; both are translated as vapor (ES) or Dampf (DE). So I wonder which concept is the untranslatable one: Steam or vapor? I would guess it is steam, but I am at a loss to justify my choice. Nor can I think of any reason for the untranslatability of the word except the fact that German and Spanish speaking people do not care for this subtle distinction.
The distinction is indeed so subtle that most speakers of the English language use both terms indiscriminately and do not care that this is wrong.
If you look attentively at a boiling kettle, you will see that it is not the kettle that is boiling, but only the water inside it.