I think that you are committed to your premise that God can't use the gift of tongues to cause a person to speak a world language which a native speaker of the language can understand, and that you are trying to fit the Scripture into it. My view is from what I see from the whole of the Scriptures and the real-life experiences of believers. It is that real-life experiences of believers speaking world languages understood by speakers of the languages doesn't fit into your preconceived premise and so you are quite willing to adapt Scripture and accuse those who testify that they have understood the language when someone has spoken in tongues, of lying.
Also, the Scripture does not clearly define what interpretation of tongues actually is. The way interpretation of tongues is used in Pentecostal churches could very well be a guess in the absence of a comprehensive user manual of how the gifts should be operated.
We have only two main references concerning tongues: What happened on the Day of Pentecost which was quite unique, although Peter says that what happen at the house of Cornelius was the same as what happened at Pentecost, which implies understandable languages (maybe Hebrew because Cornelius' family would have been able to speak Latin and Greek but not Hebrew, while Peter and his team could. But then that is a guess based on what Peter described to the other Apostles in Jerusalem. There is no indication that the 12 Ephesian disciples spoke understandable languages when the Holy Spirit fell on them. But the record stated that they spoke in tongues and prophesied, which could imply that tongues and interpretation were manifested, but we are not told that clearly.
The other reference to tongues is 1 Corinthians 14. There is no mention of anyone speaking in tongues and being understood by anyone in the meeting. That is understandable, because there were only Jews and Greeks in the meeting. So Paul is correct when he says that someone speaking in tongues could not be understood by anyone except there was an interpretation. But the tongues spoken in the Corinthian environment were not the same as the Pentecost environment, because the manifestation was different in each environment and for a different purpose. Tongues at Pentecost were a sign to the unbelievers, while tongues for the Corinthians were for personal prayer to God, unless spoken in conjunction with interpretation.
Although we don't see any reference to spoken tongues being understood by anyone, except for the crowd on the Day of Pentecost, we can use the evidence of church history and the history of the Pentecostal movement to show that the experience of the Day of Pentecost has been repeated from time to time. Every time it has happened it has been for a definite purpose and mainly around getting individuals and groups to turn to Christ.