It is important to realise the way in which this powerful novel represents a criticism of the American Dream, the impulse that brought so many immigrants from all over Europe to the West, like the Shimerda family. The idea was that America represented a melting pot of all different cultures and backgrounds, where individuals lost their difference and assumed some kind of vast, all-consuming homogeneity that would create a new universal culture through the erasing of the old separate cultures of all the different people and their backgrounds. Therefore, the fact that the narrator reports how Antonia hardly ever speaks English any more and tells the reader how her children grow up speaking Bohemian is a criticism of the American Dream. Note what Antonia says to the narrator:
"And then, I've forgot my English so. I don't often talk it any more. I tell the children I used to speak real well." She said they always spoke Bohemian at home. The little ones could not speak English at all--didn't learn it until they went to school.
Antonia's reversion to Bohemian therefore highlights the limitations of the American Dream and also the characters who have been crushed by it, like Antonia's father and various others.