It is a big subject. Skeptics use circular reasoning, when they say that something happened, therefore it wasn't impossible. It does nothing to determine whether there was supernatural intervention in either the event, or the fore-knowledge of the event. These "signs" are not impossible; they are unlikely, sometimes extremely unlikely. Joseph Smith led a band of 200 men, called Zion's camp, back to Missouri to confront the anti-mormon mob. When Zions camp ran out of drinking water, it was a serious situation, as there were no rivers nearby. Joseph Smith took a shovel and went out into the prairie and dug a one foot hole. Enough fresh water came out to fill every container in the camp. To the members of the little army, it was equivalent to Moses hitting the rocks with his staff, and providing water to the children of Israel. Personally, I've dug many holes, and never got so much as a drop out of them.
These studies are studies of the fake stuff. I did warn you that there were people who just babbled. Yes, there are recorded and verified events where someone without training has spoken another language. There are many such stories in Mormon history. I myself have experienced it, although I did have some training. When I served a mission in Peru, I had taken 1st year Spanish in High School. I was a long way from fluent. I barely passed the class. When I spoke my best Spanish in Peru, people stared at me in total incomprehension, as if I was still speaking English. It was very frustrating to say the least. My companion would end up doing almost all of the talking. Then one day, while teaching this one family, I could suddenly speak this fluent Spanish, and I saw comprehension in their eyes, and I also knew what I was saying. I was amazed. The next day I went back to speaking in my clumsy North American way. It was several more months before I could speak clearly enough to be understood, and then only at the level of a five-year-old. I know it is subjective, but I was there and I know that something happened, and I will never forget it.
I know it is subjective in the extreme. I also know it happens, because it happened to me. I have stood in front of a large group, without any preparation, and been told word for word what to say, by some unseen force. The spirit was so strong that some people were moved to tears. I'd like to take credit for it, but the words didn't come from me.
Do we live on the same planet? Go to any Mormon church, and ask if anyone was ever healed of a major illness. I'll bet you get at least two or three. I myself was given two years to live by doctors some 15 years ago. The disease, which was untreatable and had 100% mortality, was completely gone just a few months after diagnosis, along with all the symptoms - and after a priesthood blessing. I have taken the tests twice in subsequent years to verify the result. I am not alone. Mormon history includes people who were cured of blindness, small pox, and some have even brought back to life. I recently read the story of one man (I don't remember his name; forgive me. I am terrible with names) who was told by six different doctors that he would soon die. He couldn't even walk. Two Mormon missionaries gave him a blessing and cured him. He lived a long and happy life after that. Shortly after his baptism, the Holy Ghost came to him and told him to move to Kirtland. It was the middle of winter, and esteemed foolish by many to make the trip in winter, but he was compelled to move with urgency. As it turns out the church was in danger of losing their property, on which they were already building the Kirtland Temple. The loan for the property was due, and they had no money with which to pay it. On the very last day before the land would have reverted to the previous owner, the man who was healed showed up, having just moved into town, and paid the loan in full. Signs follow them that believe.