Alan Mackenzie wrote:
> Up till now, all messages output have been ASCII (with the exception of user
> supplied characters and in some other rare instances such as outputting
> `sentence-end').

No, even the current stable version of Emacs (24.4) regularly outputs curved 
quotes on typical displays.  I just now ran emacs -Q, typed "C-h i m emacs RET", 
and saw curved quotes on the first screenful of the Emacs manual.  So we're not 
making such a drastic change here; we're just evolving Emacs in the natural 
direction.

> does the code test the output
> display setup to decide what sort of quotes to output (best), or is it up
> to some user option (middling) or is it hard coded (worst)?

It tests the output display setup.

>> This is not too much to ask of an Emacs developer.
>
> Of course not, but could it be too much to ask of an Emacs user?

Emacs users in 8-bit environments shouldn't need to worry about this; they 
should just see straight quotes where the Emacs manual etc. uses curved ones. 
This thread is more about the special case of a developer who's using a Linux 
console that doesn't support the full Unicode gamut.

> this warrants an extensive entry in NEWS.

Makes sense, and the next iteration of this patch will add a NEWS entry.

> I don't think that's the font for me.  It has one-pixel thick spidery
> characters, rather than the two-pixel thick ones the default fonts have.

The font has a bold variant.  I'll attach Lat15-TerminusBold16.psf.gz.  There 
are other variants that are even bigger, if you like.

> ... Its apostrophe is a vertical line rather than a top right to bottom left
> sloping character, and I find its curly single quotes too indistinct

If you just want to continue to use the same font, how about the attached font 
lat1-16.psfu.gz instead?  It's taken from the current stable version of kbd 
<http://kbd-project.org/>; see 
<http://kbd-project.org/download/kbd-2.0.2.tar.xz> and extract the file 
kbd-2.0.2/data/consolefonts/lat1-16.psfu and then use gzip to get the compressed 
version.  This handles curved single quotes and if it's the same lat1-16 font 
you're used to you should find it comfortable.  Curved double quotes don't come 
up as often, but if you want them to be displayed using a graphical 
representation other than '"', you can do something like the following:

(printf '0x0d3 U+201C\n0x0d9 U+201D\n'; psfgettable lat1-16.psfu) |
psfaddtable lat1-16.psfu - lat1-16-double.psfu
gzip -9n lat1-16-double.psfu

and then use the font lat1-16-double.psfu.gz instead.