Unless it's Asgardian, Sylvie doesn't know either, but she picks a wine anyway, mostly at random. The waiter can tell them if it's any good or if she's picked something awful, but then, of course, she'll just be annoyed with the waiter.

"Then don't," she answers, looking up at Bucky again, her eyes lit up. "We don't have to choose."

That's the point of a place like this, as far as she understands. They can have whatever they like and then some.