That text is actually quite misleading. It never says that it's the snake that should be thought of as figuratively, maybe it's the Tree or eating a certain fruit that is figurative.

True - any part of the described incident (more likely, all of it) could be figurative.

The devil is a being of "pure spirit" and the catholics believe that he was an angel that disobeyed god. Now, this fallen angel somehow tempts the first parents, who are in a garden (378). It could presumably only be done in one or two ways: Satan talks directly to Adam and Eve, or he talks through some medium. This medium doesn't have to be a snake, it could have been a salad.

Not necessarily. Communication does not need to be verbal. The temptation could have appeared in terms of, say, the manipulation of coincidence. Or, as you put it, a spirit that tries to make people do bad stuff.

But yes, there is definitely a Tempter there; some sort of malign intelligence that tries to persuade people to do Bad Stuff. That is a fairly well-known part of Catholic theology, commonly known as the devil.

But, they don't even say that the snake isn't real.

The Vatican tends to be very, very, very, very cautious about definite statements of any sort. As in, they prefer not to make them if there is any possibility at all that they might be wrong.

And hey, small though the probability appears, maybe there was a talking snake...

I agree there is probably someone who says that evolution is true and that people evolved from monkeys. But, to compare likes with likes here, you would have to find a leading evolutionists that said this, to compare with these leading christians that believe the snake was real:

Would I need to find leading evolutionists, or merely someone who claims to be a leading evolutionist? The second is probably a lot easier than the first.

If so, can you find any popularizer of evolutionary theory that says that man evolved from monkeys?

My googling is defeated by creationists using the claim as a strawman.

...to be fair, I didn't really look all that hard.