Two symbols in description of one of the challenge
Good evening! I'm so sorry for possible mistakes, I'm writing using a translator. In Russian translation of challenges, description of one of the challenge displayed as two symbols and it is not possible to determine what required from the player to complete it. I also don’t know if this bug belongs to the bug section, but just in case I inform you about it. Thanks and have a great day! Platform: PC Steam version of game :)

Comments
Just to let you know, in case it's helpful for completion purposes, I think that's the challenge which requires you to damage five different generators in a single game.