Before you act powers can affect other characters, such as "Before you act, each character at this location must..." But, I think you are saying that the "you" in the Goblin Warchanter's power is the person encountering the card. This FAQ from the Paizo site explains that:
So, everyone that wants to play a spell with the attack trait or a weapon with the Goblin Warchanter will need to succeed at that check. Obsidian has said that the way it works now is temporary and they want to implement a way to do it only if you really want to play a spell with the attack trait or a weapon, so the implementation is a sort of stop gap solution.
