Best way to depend on the user's charset

[Akim Demaille]

Hi (Bruno)!

I would like to use "•" in Bison's output messages when this character is 
available.  For a similar purpose, we already have this:

#. TRANSLATORS: This is used when a line is too long, and is
#. displayed truncated.  Use an ellipsis appropriate for your
#. language, remembering that "…" (U+2026 HORIZONTAL ELLIPSIS)
#. sometimes misdisplays and that "..." (three ASCII periods) is a
#. safer choice in some locales.
#: src/location.c:252
msgid "..."
msgstr "…"

So I plan to map _(".") to "•".

But I see that currently English does not even show on the translation project 
for Bison (likewise for gnulib).  Besides, I don't know what English-speaking 
people usually use for their locale.  I guess C.UTF-8 is not unfrequent.  But 
it's a pity not to use "•" when it's available and to fall back uselessly to 
".".

So my question is: what is the recommended way to address such a case?

Currently my favor goes to adding an en.po myself in Bison and to deal with "•" 
there, too bad for C.UTF-8 users.  Does that sound right?

Thanks in advance.  Cheers!