I think that there are two possible answers for this. You can call Christians who engage in speaking in tongues and other such activities "Pentacostal" or, more broadly, you can call them "Charismatic."
Charismatic Christians believe in a very emotional religion with a strong personal connection to God. They believe that God still acts directly in the world. By this, I mean that they believe that God still performs miracles by involving himself in the physical world that we all live in.
One manifestation of this sort of miracle is the gift of speaking in tongues. Charismatics believe that God bestows this gift upon people who have true faith in him.
They are called pentecosts,I used to be one and never really understood why they would scream things that they dont know what they are even saying. I asked this girl and she said its our way of speaking or god,and I said well you know in the bible it says God used the holy spirit on Jesus after he was batized and he went preaching in languages he actaully understood and she's like noo thats wrong.How is it wrong if thats what t says in the Bible and she says she reads the bible but I guess people understand it they way they are comfortable but I or Jehovah Witnesses we dont get the book to out comfort we just do exactly what it tells us to do,I even had scriptures to prove to her and she's still not accepting it, the other day i was talking to a guy and he asksme what my religion is and I tell him and he's im sorry but im not allowed to speak to you, I said why and he's like my church doesnt allow it and he was a pentecost,so is my aunt and her family and they do the same with us. It's like thats what they teach everyone there.Is that what Jesus did,did he ignore people because they didn't follow him?