Keep the Heroes Out! cards have no text at all. As such, with just the rulebook you will be able to play the game in all supported languages.
Inside the box the rulebook and dungeon book will be in the English language, but through Boardgamegeek you will be able to download the rulebook in all of the following languages: English, Portuguese, French, German, Italian and Spanish.
Unlocked scenarios: Scenarios unlocked during the campaign may contain spoilers and/or follow up stories to previous scenarios, so read it at your own risk: