It's not just one country in terms of language. There are lots of little variances here and there which provide certain signals. For instance, the big freeway

It's not just one country in terms of language. There are lots of little variances here and there which provide certain signals. For instance, the big freeway is just "101" around here. However, in Southern California, the same route is frequently called "the 101". They tend to use "the" in front of the numbers for whatever reason. There are many of these things which can give you some insight on someone's background. Is it soda? Or pop? Or "coke" as a generic term? Do you use "hella" or "wicked" as a modifier, as in "hella cool" or "wicked fast"? There's the whole "ya'll" thing, and don't forget "all ya'll". Are you "fixin'" to do something? How about "ain't" and "busted"? This is just word choice. There are all sorts of different ways to pronounce the same words, too, and those also give you some idea of where someone might be from.