"The merchant sells meats."
Translation:Mercator carnes vendit.
It can, if you sell different types or cuts of meat; the same way as you can say "peoples" if you are talking about more than one nation, even though "people" is already considered a kind of plural. Although it is probably more often simply treated as a mass uncountable noun.
In Latin, however, when you sell meat in general, you must sell it in the plural, unless you are referring to a specific piece of meat that is being sold; then you would have mercātor carnem vēndit.
Yeah. Both carnivore and carnivorous come from "caro, carnis" (meat) and "voro, vorare"(to eat)