There are many settings in fantasy and sci-fi where characters can visit a new world and can understand an indigenous population that they have never even heard of before. Some fictional universes have ways of adressing this, e.g universal translators in Star Trek and the Babel Fish in Hitchhikers guide. How necessary are such plot devices? Or if it's not explained is it the sort of plot hole most readers will turn a blind eye to? Are fantasy readers going to be more forgiving of this than sci-fi readers? I ask because currently my fantasy novel with touches of science-fi has no explanation for why characters from another world speak English. I have thought of a solution to this, but it would require some anniying reworking, which I don't want to bother with if no one would care.