I believe that tongues are a language spoken somewhere in the world. It is just that they are not learned by the speaker but is inspired by the Holy Spirit. I don't believe that they are heavenly languages because why have multiple languages in heaven. It is interesting that before the tower of Babel, there was only one language spoken, and the only reason for the institution of multiple languages was to counter the pride of man. It is also believable that the language Adam and Eve spoke was the same one that God and the angels spoke, because before the Fall, Adam and God had fellowship together. Also, the snake spoke the same language as Eve. So, to say that tongues is one of the languages of heaven is pure fantasy. When Paul said, "Though I speak with the tongues of men and angels" he was not talking about the gift of tongues at all. He was saying that even though he was the most eloquent man in heaven and earth, if he didn't have love he would just be an empty noise.
Also, in 1 Corinthians, when Paul was writing about tongues, he implied that tongues was a world language, because he said that there are many languages in the world. That's enough of a clue for me that tongues is a language spoken somewhere in the world. There is enough proof for me that modern tongues is a world language through the actual events that took place in my own church during the 1970s, where a close friend in a prayer meeting of over 20 people, spoke in tongues, and a Ghanaian visitor told him that he was praising God in his own rural village dialect, a language my friend, who had never been outside of New Zealand could never have known. Also, when I was praying in tongues quietly in a church service, a New Zealand Maori lady sitting beside me told me that I spoke encouraging things to her in fluent Maori language. Even when I learned basic Maori some years later and tried to speak it to my 10 year old pupils in class, a bilingual boy just rolled around laughing at my mispronunciations.
Now, the catch 22 situation is this - either one has to acknowledge that modern tongues can be an understandable language in some circumstances where there is a hearer native in that language, but unlearned by the speaker - or that my friend, the Ghanaian visitor, 20 people in that prayer meeting, the Maori lady, and me, were all lying for the sake of supporting the truth of modern tongues.
I put this same question to anti-tongues members on two other forum sites, and they never replied. I suspect they were flummoxed. I think that the honest comment from an anti-tongues person is to say "I don't believe in modern speaking in tongues", rather than teach others that it is false and not for today. That way they are stating their own opinion, and not setting themselves up as an arbiter on what is true or false in modern Christian worship.