Asterix & Friends currently needs the Adobe Flash Player to run on PC in the browser. Unfortunately more and more browsers are de-activating flash support which makes the activation more complex. You can find the detailed steps how to activate Flash here: https://www.asterix-friends.com/de/adobe-flash.
We are currently working on a version of the game that runs on the Unity engine and therefore does not need Adobe Flash to run. Until it is released you may also try the game inside Facebook Game Room or on iOS and Android devices.