This sandwich is not tasty would make more sense.
And do you remember how to say that po polsku?
Ta kanapka jest niedobra
I'd say "spoiled" and would even accept that as a correct translation...
one of the definitions given for 'zła' is 'wrong'. could this also mean 'this sandwich is wrong'? duolingo didn't accept it.
(also... 'ta kanapka jest zła' could mean 'this sandwich is evil', right? :p)
Evil, bad and wrong - all translate to zły. But that doesn't mean that you can use them interchangeably, sandwich cannot be evil. Nor wrong (unless it's a Disney character ;-) ).