The Bible refers to people speaking in tongues--most notably at Pentecost. Is this something that legitimately happens today?
Paul says when he was a child he spoke like a child. He was comparing tongues use to young church use.
1 Corinthians 13:9-10 NET For we know in part, and we prophesy in part, but when what is perfect comes, the partial will be set aside. When I was a child, I talked like a child, I thought like a child, I reasoned like a child.
I've been in church services where speaking in tongues has happened, but it always seems weird and creepy, and those doing it seem like kooks. How can I know if this is legitimate, or if I'm right in thinking it's strange?
Everyone is kind and nonjudgmental, and would not like to criticize a practice adopted in other churches. I believe that is about right. Those who follow Christ must search for truth. It's a requirement :
Luke 11:13 NET If you then, although you are evil, know how to give good gifts to your children, how much more will the heavenly Father give the Holy Spirit to those who ask him!”
Young churches are ministered to by God:
Luke 22:35 NET Then Jesus said to them, “When I sent you out with no money bag, or traveler’s bag, or sandals, you didn’t lack anything, did you?” They replied, “Nothing.”
Jesus's faith provided teaching and supplies. The perfected church, the mature church will manifest it's own faith. To reach maturity, they must sell even their most precious possessions :
Luke 22:36 NET He said to them, “But now, the one who has a money bag must take it, and likewise a traveler’s bag too. And the one who has no sword must sell his cloak and buy one.
Much sacrifice is involved in transmitting the word of God :
2 Corinthians 4:12 NET As a result, death is at work in us, but life is at work in you.
John 15:13 NET No one has greater love than this – that one lays down his life for his friends.
1 Corinthians 13:11-13 NET But when I became an adult, I set aside childish ways. For now we see in a mirror indirectly, but then we will see face to face. Now I know in part, but then I will know fully, just as I have been fully known. And now these three remain: faith, hope, and love. But the greatest of these is love.
John 14:12 NET I tell you the solemn truth, the person who believes in me will perform the miraculous deeds that I am doing, and will perform greater deeds than these, because I am going to the Father.
Teaching mature doctrine requires great effort, risk and love, since there could be rejection, even when the text supports your view. Death in us, life for the objectors.