Then call them Sheffield United like everyone in England has done for ever.
It's a bit like if people woke up one morning and started calling Bayern 'Bavaria'. You'd know what they meant, you could even argue that it makes sense because we translate München to Munich so why not the first half of their name, too, but it's just wrong. Sheffield United have been Sheffield United for ever, to hear people drop the United just sounds appalling. And it's five letters, people have spent longer replying to this thread telling us how much time they've saved than they ever would have spent typing out those letters.