Tongues were:

Real languages

Acts 2:1-11 - The apostles speak in tongues on the day of Pentecost. The tongues they were speaking in were real languages that people from other nations could understand immediately.

Acts 10:44-48 - The Gentiles were given the ability to speak in tongues.

Glossa (tongue) in Acts 2:4 were used interchangeably.

I Corinthians 13:1-3 - Are the gongues of angels necessarily unintelligible? Also, the main point of this scripture is the importance of love. All these examples are hypothetical exaggerations.

To edify through understandable communication

I Corinthians 14:1-26

I Corinthians 14:5.

I Corinthians 14:6 - The emphasis was on understanding the tongue.

Able to be controlled

I Corinthians 14:27-33

Limited to the first century

I Corinthians 13:8-10 - Spirigual gifts would be done away with. What is the “perfect” that was coming? “Perfect” here is teleos, which means perfect in the sense of complete. Paul wrote this looking forward to the time when revelation would be complete - when the New Testament was complete. Spiritual gifts were present in the first century to show the authenticity of the word until revelation was complete.

Compare Biblical teaching with modern-day practices.

Is it a real language?

Is it edifying others in the assembly because it is understandable communication?

Is it controlled?

No modern day tongue-speaking is in the first century.