"I've heard that some people with the gift are actually speaking other languages they have never heard and there is an interpreter there to say what it means."
Yes, this is also true. Have you ever read "They Speak with Other Tongues" by John Sherrill. When he started writing the book he was a skeptic about tongues. He did much research for the book and gives examples of what you mentioned. The Holy Spirit put him in situations where this was happening as he wrote the book. The book is awesome. The book turned out to be nothing like what he intended because before he finished it, he not only believed in speaking in tongues, but also received the gift himself.