Eli Zaretskii wrote:
> I fear it will just be a source of confusion.

Well, 8-bit terminals are no longer that common (at least when developing Emacs) 
so it's no big deal either way, and as it's easier to do it without highlighting 
let's try it that way.  A proposed patch is attached; it worked for me.

Stefan Monnier wrote:
> The real test is when the environment
> uses utf-8 but the terminal's font fails to include the glyphs.

That can easily happen with other characters, but in practice nowadays I think 
everybody has glyphs for curved quotes.  This is in part due to Microsoft 
Windows putting curved quotes in their most-popular 8-bit character set starting 
with MS-Windows 1.0 in 1985.  This put a lot of pressure on everybody else to 
support these glyphs one way or another, and it has been thirty years now....