1975 for me.
Because people have free will. God does not force anyone to speak in tongues, nor will He force the person to interpret. People need to be taught, which Paul was doing in his epistle.
Some legitimate languages are very simple.
It's the PERSON speaking in tongues to God.
1 Cor 14:28 But if there be no interpreter, let him keep silence in the church; and
let him speak to himself, and to God.
Scripture?
Again, is there a scripture that says when a person speaks in tongues in the church it is the Holy Spirit speaking TO the church? 1 Cor 14:2 explicitly states that when a person speaks in tongues he is speaking TO God.
My church used to believe as you do, that prophecy and interpretation of tongues was essentially the same thing: God speaking to the church. But there is no verse that says when a person speaks in tongues it is God speaking to the church. It's not there. 1 Cor 14:2 says that when a person speaks in tongues he is speaking to God. Acts 2:11 says that the apostles were speaking the wonderful works of God. Acts 10:46 says that Cornelius and his family were magnifying God. 1 Cor 14:17 says that when a person speaks in tongues he is giving thanks well. If those are the things that the Bible says speaking in tongues is, then the interpretation of tongues should reflect that.
I believe those two manifestations are God giving you information (knowledge) and what to do with it (wisdom) in situations that you wouldn't know anything about by your five senses. It's revelation from God.
Sometimes it works, sometimes if we're not careful it turns into hacking each other up.