In this case, it is literally a legendary trailer.
Some time ago, Pokemon Sun/Moon got an incredible, hell of a trailer- it was a trailer that showed off loads of footage from the game, as well as new locations and story details, all set to a rousing musical score. And while the trailer was great and could be enjoyed by just about everybody, a lot of its nuance was missed, because the text in the trailer was all in Japanese.
Now, however, it seems like the trailer is available in English at last- meaning we get to see a lot more of its story than we had before. The trailer delves more into some in game mechanics (such as what seems to be replacements for the HM mechanics from the previous games), as well as story details (including the Ultra Beasts), and of course, some great footage from the game.
Pokemon Sun/Moon are due out on Nintendo 3DS exclusively on November 18 in Japan and North America, with the European release following on November 23.