Rowling casts Brits only. The only exceptions are the students from the other wizard schools in Europe -- Beauxbatons and Durmstang. French actress, Clemence Poesy, plays Fleur Delacour. The girls playing her classmates might also be French since they come from the French Wizard School, Beauxbatons. Stanislav Yanevski, the young man who plays Viktor Krum, is from Bulgaria and I'm sure they cast his classmates from there as they hail from Durmstrang. Although they don't tell us where Durmstrang is located, you can assume Eastern European [Bulgaria?]area. The Tri-Wizard tournament involves the three European Wizarding schools. Therefore, they cast only those roles outside of England but exclusively Europe for representation of those schools.
The US has not been brought into any of the books and since Rowling wants only Brits in the films, you can count on zero chance of an American being in the film. There are plenty of Brits to cast from, I'm sure.
The US has not been brought into any of the books and since Rowling wants only Brits in the films, you can count on zero chance of an American being in the film. There are plenty of Brits to cast from, I'm sure.