I can speak in tongues and also interpret. I normally speak in tongues when I'm alone and I am interceding in prayer for someone. Sometimes God will put a person in my heart to pray for. Then I pray in tongues and God shows me exactly how to pray for an them. There have been many times where I later see those same people and they share with me that same struggle that God had revealed to me in prayer. I don't tell them though-- It's exciting to know that I prayed the right prayer!
Every now and then there are people in church who speak in tongues and have no interpretation. There are a couple of women in my church who interpret for them. I don't publicly speak in tongues nor do I interpret. However, right before someone is going to interpret a word from God publicly, I quietly speak in tongues and wait for God to reveal the word to me as confirmation. Once again I don't go announcing it to everyone, it's something that's between me and God. I don't feel led to tell my pastor that I can interpret tongues.
However, only once did God ever want me to give someone a word from him. In my previous church I was at a women's prayer meeting-- we were praying and some of the ladies were speaking in tongues. God gave me a word for some woman and He wanted me to speak it, so I did. This woman started balling because it was an answer to her prayer. It was a blessing because I had the privilege of seeing God actually manifest that word in this woman's life.
I believe this gift is meant to edify the body of Christ. I do feel that speaking in tongues out loud with no one to interpret is pointless. Praying in tongues between you and God is a beautiful thing. Sometimes people are given this gift and can't interpret because the person hasn't matured in the gift. I was given the gift of tongues when I was about 12 yrs old. I was in church when it happened and no one made me do it nor did I even ask God for it. I didn't even no it was a gift At the time I couldn't even interpret what I was saying. I remember the first time I spoke in tongues and my friend was standing next to me. She was shocked and told me she had no idea what I was saying. She even tried to copy me, but it didn't quiet sound the same.
I never told my parents about that experience. Then when I got in my twenties I could actually hear the voice of God give me a word in my spirit. I didn't know it was him till I started getting confirmations through the word, songs, and sermons. I was amazed that I was hearing from God and that it wasn't something I made up in my head.
I know this gift doesn't make sense to people, but God is very complex and none of us will ever fully understand him. Another thing I've learned about this gift is that God usually doesn't have you give someone a personal message that he didn't already reveal to them first. So if someone says they are giving you a word from God, but God never revealed it to you first, then be careful about receiving that word, especially if it's something negative.