One of the oldest open-air markets in the country has evolved into a cultural cornucopia. It is not your parents’ or grandparents’ Haymarket.Consider it now the United Nations of Haymarket.Throughout the 20th century, most of the vendors were Italian. Now, vendors from 20 different countries sell fruits, vegetables, and seafood on Fridays and Saturdays. The clientele is equally diverse.Mustafa, 96, and his wife Sede, 82, of Iran navigate over the cobblestones with a food cart and a cane.“It’s a good thing,” says Otto Gallotto, president emeritus of the Haymarket Pushcart Association, formed in 1820. “I have a Haitian, two El...