How do you imagine the various tribes around the states is like? And will we possibly encounter one in the new enstalment to the series?

I would imagine they are like many of the other tribal people we have seen in the Fallout series. Primitive weapons, tattoos, tribal art, worshiping nature or pre-war objects and little communication skills.

I doubt we will see tribes similar to the ones on the west coast in Boston. Tribes are usually very low tech and build everything from scratch off of wild lands. Boston is a dense cityscape, so we will most likely be getting small towns like in FO3.

There might be the possibility of tribal villages in the fringes of the Boston area as we get further away from the city.

Tribes develop tribal qualities because of their isolation from other groups. Look at the Boomers. They may have some good tech, but the worship their weapons and dream of flight. You can see how unique they are through the way they have customized their vault suits with flight jackets and other pieces of flair. The more isolated a group becomes, the more they seem tribal or even alien-like to other groups.

Boston is a big city with a lot of groups interacting with each other. Even if they fight one another, they are still interacting and begin shaping each other's identity. Much like how the different sub-factions of the BOS are each defined by how they treat other groups.

With so many groups interacting, a common language is needed for communication. An isolated group will inherently develop new languages because they don't need to talk to anyone else. Boston will be too densely populated to create new languages. However there maybe new colloquial terms that each group develops and introduces into the English language.

TL;DR: It's not likely we will see anything like tribes in Boston, but we'll never know until the game comes out. There be villages on the edges of the map, I don't know.