Definitely number two for me. Not merely due to my love of Sci-fi but because of the opportunity that it would present, the ability to experience history and the future. Text books can only give an insight into history but being able to live it would help cement understanding of the events and a better understanding of how the present was formed. Also you could have great fun confusing the archeologists, dropping a floppy disc into King John’s tomb, putting a signed photo of Roger Moore’s James Bond into Da Vinci’s collection…
There is the other side too, I could give some closure to those who deserve it. Example in mind being Rebecca Nurse who was the principal victim of the Witch Trials of Salem. I could show her that her plight was not forgotten, though I do wonder what she would make of the tacky witch based tourist attractions.
The other two I think would be powers which would undermine the human psyche and therefore could not be classified as a superpower. To make two people agree would no better than totalitarianism, there would be no benefit to either party. We need disagreement in the world and too force agreement would stifle progress.
Again learning a language is another way we as a species get to understand one another, language is more then just a means of talking and writing, but an expression of ourselves.