There was a huge push among many of the immigrants of that era - especially for children, like Vito - to learn English, even if they had to study on their own or at night school.

By the 40's when the first movie opens, Vito and his family (and probably most of his friends), have moved beyond their early immigrant stage. They're no longer living in the middle of tenement housing with other people who came to American from the same type places. They've made money. They've bought houses. They're becoming more Americanized.

At this point, like many immigrants, they're trying to fit into the larger picture of America in many respects. They've kept their religion, their food, and many aspects of culture, but as far as language goes - it's part of the past, not the present. And these are people who live in the present moment, in my humble opinion.