My Suzi is not too much of a barker, but, she does when she wants something. Toy dogs are notorious for barking though, but, A yorkie usually has a smaller bark, but they can be yappy at times.
I think it is all about the way you train them too. AND how much time you spend with them.
I am at home all day , mostly 24/7 with Suzi . I believe that is why she does not bark too much.