I have never spoken in tongues myself, but I do believe that there is a real gift of speaking in tongues. There are also demonic tongues, and we can make up languages as well. I used to make up my own languages when I was a child, which sounded a lot like the type of tongues we see in some videos, and I have spoken in demonic tongues, which is also common in some videos. What do these two situations have in common? Disorder and chaos, no good Scriptural foundation.
But I have also heard true tongues being spoken, which were definitely from the Holy Spirit, spoken by those who truly know the Lord and His Word. There was nothing demonic about it. I haven't gotten the gift myself, because I have been urged by God to study the Bible a lot more when I have prayed about it.
What I do see among those who claim that all tongues are demonic is a deep fear of the devil. We live in times of great deception, with many false teachers and false prophets, doctrines of men and doctrines of demons, but God is still sovereign. He is still in control. If someone earnestly seek Him and study His Word, He will respond, He will lead us and teach us. He will intervene in our lives, and He will not let the devil deceive us for too long. Those who say that all tongues, all gifts, are of the devil are giving way too much power to the devil. He is a real foe, and he has real power, real signs and wonders, but he is nothing at all compared to God. If someone fears the Lord, they don't need to fear the devil, because God will strengthen and protect them, keep them alert and awake.
Out of all the gifts, the gift of discerning of spirits is the most important one, and usually the last one people seek unfortunately. But that gift (and I have it myself) reveals whether something is of God or not, and we should all seek it, and put all of our faith and trust in God.
Pointing at everything that you disagree with, saying it is of the devil is idolatry, because you are making the devil bigger than God, taking what is of God and claiming that the devil has done it. You are lowering God, and calling Him a liar, and elevating the devil, putting a whole lot more faith in him than in God, fearing him a lot more than you fear God.
If we see someone preach the true Gospel (Jesus Christ, the Son of God, Messiah, Word of God come in the flesh, who died on the Cross for our sins and rose again and conquered death, grace through faith, repentance and death to self, baptism, sanctification, saying that we should study the entire Bible, no false doctrines etc), and Jesus saves a lot of people through that person, no one would say that is the devil doing it. But then the one preaching prays in tongues, then suddenly the devil was behind pointing a lot of people to Christ, preaching sound doctrine? It makes absolutely no sense.
I have cast out many demons by the Spirit, and seen people be set free by Jesus Christ, and of course the critics come running saying it was of the devil (which may be the unforgivable sin btw). Same with healing, a gift that God has given me. Someone was miraculously healed, praise God! BUT, some doctrines say that the sign gifts no longer exists, so of course that was the devil... ???????? People, stop taking what is of God and claim it's of Satan! It makes no sense, and it is idolatry! The devil would never, ever want anyone to be saved by Jesus Christ!
We have to judge a tree by its fruit, not by signs and wonders or lack thereof and not by works. If a person's spirit points people to Jesus, calls Him Lord and does what He has commanded, shows the fruit of the Holy Spirit, preach repentance from sins and everything else that God has commanded us in Scripture, that is the Holy Spirit. If it doesn't, it is NOT the Holy Spirit. If the one with the Holy Spirit does something that you are unfamiliar with or unsure about, don't automatically claim it's of the devil.
The way I see it, if someone seeks signs and wonders, or their own will and their own glory and their own name known, they will find the devil. But if someone seeks God, His will, His glory and to make His name known, they will find Him, and if it is His plan for them, signs and wonders may follow. They did for me. Now, if anyone wants to test my faith to see if I'm a true Christian, go ahead! I'm not perfect in any way, but I know Jesus. I surrendered my entire life to Him and I have chosen to live according to His will, for His Kingdom, for His Name the rest of my life, because I know that God and the Gospel is all that matters. It is His will be done, which I pray every, single day and mean it. He gave me some gifts and some signs and wonders follow me where He leads me. If you want to claim that the devil is doing them (healing, casting out demons, stopping the rain and the storms, etc) go ahead, but that isn't going to change what God is doing.
We all have to be very careful in our faith, making sure that we are led by the Word and by the Holy Spirit, and also make sure that what we see is of God or not. But we also have to make sure to not end up in fear, thinking that everything is of the devil.