"Diese Nachricht ist wohl falsch."
Alright, I "surrender" on what I've said b4. "Must be wrong" is a little too much, misleading or even incorrect, but "This news seems to be wrong, or is likely to be wrong, or is perhaps wrong" are definitely the right ways to translate this phrase. I am native German and speak English as first language for quite a while. To the question how would it sound to express certainty, well you would say in German: "Die Nachricht ist falsch", that simple, that leaves no room for questions or uncertainty. ENG: The message is wrong.
OK, I think I get what you're talking about. In English, one might say something like "This must be wrong" to reflect disbelief, skepticism, strong surprise. It's a form of hyperbole--you haven't exactly said what you mean, but rather exaggerated for emphasis.
But I think it would be impossible to build that nuance of spoken English (which would probably best be conveyed in context) into this one-sentence exercise so it makes sense. It might not cross cultures--I don't know. In any case, it might rather puzzle quite a few people if Duolingo were to suggest that "This news is wrong" is exactly equivalent to "this news might be wrong."
Well said, I wasn't quite happy when I finished typing. You pointed it out correctly, if there is some skepticism/disbelieve in it I would still say, "That must be wrong" with an inflection of disbelief of course. Nuff said, it should be all clear "as mud" now, as the Aussies would say. ++++++++++++++++ UPS, just got an email from Duolingo, saying that they accept my version: "This news must be wrong" as a correct answer. What have I done? We should point Doulingo to this thread, I is only right with the inflection of disbelief. Bugger