What does it mean when a couple dresses alike, and speek alike?

It's actually a very natural thing. We tend to mirror the actions of those we like, usually unconsciously, because it helps them relax and you both feel that you understand each other better.

Speaking similarly may mean that they do have similar backgrounds, but they may not. It may just mean they already know what the other person is thinking about and can anticipate their words. Repeating words after the fact is like mimicking actions.

Dressing alike may mean they are involved in similar activities, but that may also mean they have just fallen into a pattern of what clothing they buy.

They have been together for along time or maybe they have the same sense of style and that's what attracted them to each other I don't know.

They have spent a lot of time together and personalities are very similar. Probably had similar environmental experiences growing up.

Well,...

It means they are creepy. No, seriously, I think it means they are trying awfully hard to prove to the rest of the world that they belong together and I would wonder if they really believe they do themselves?

They are acting like how couples suppose to act, two souls that become one, better watch out for marriage

It means they have poor differentiation (lack separate sense of selves)

they been together for a long time

They may be twins

That they are really bored and have no character, and very stupid..