This Poll Is All About First Impressions: 20 Images & You Have To Match A Face To A Name – No Wrong Answers

In UK English you wouldn't say "how would you call them" you'd say "what would you call them", as Lakota says. How implies method.

UK here: did the character say 'what they're called', or 'how they're called'? It's the 'how' not the 'call' which grates. 'What would you call them?' is correct for the question intended here, but 'How would you call them?' doesn't mean 'What name would you give them?' - it's 'What method would you use to attract their attention?'.

I'm American, yes. I have heard people say someone's name and mention it's WHAT they're called, but not HOW they're called. Saying "How would you address this person?" as a sentence makes sense and is acceptable. It implies name/title. "How would you call them?" does not imply you're asking for their name/title, it implies "in what manner/by what means would you call them?" Hence me saying "mouth/telephone" - since the sentence is asking me the means by which I'd call them, not what I would call them in terms of name.

"They're called John" is a valid answer, but the answer to "What are they called" not "How are they called", which seems more of the way it's said in French: "Comment t'appellez tu?" is "How do you call yourself?"