What is wrong with categorizing by language? Brits, Americans, Aussies and Kiwis, regardless of race, congregate together wherever they are. If they decided to stay and live in a foreign country, they would become, in the eyes of the indiginous people, a single ethnic group. Only the English-speakers themselves would recognize the difference.
In the US, I see Dominicans, Mexicans, Hondurans, Panamanians, Colombians, Peruvians and Ecuadorians congregating and socializing largely in the same places. A language is a major part of the wiring of your brain. The shared language does seem to create a certain cultural adhesion.
I think people underestimate language as a cultural factor. Sure, a pure blood Inca from Peru has some very different traditions than a Dominican. But, if the Inca speaks Spanish as his first language, then you still might find him listening to Bachata with his fulanos at Jack's Pizza in Allentown, PA.
When I'm in the US, my dominos group consists of three Dominicans, a Puerto Rican, a Panamanian, a Columbian, a Peruvian, an Ecuadorian and a Mexican. BUT WE DON'T ALLOW ANY ARGENTINES!!!