Alex Kost <alezost@gmail.com> skribis:

> Evaluate there:
>
>   ((@@ (guix ui) texi->plain-text) "foo \u2015 bar.")
>
> So far so good.
>
> 2. Now connect to it, either with:
>
>    - netcat: "netcat localhost 37146"
>
>    - or Geiser: "M-x connect-to-guile"
>
> and evaluate the same expression.  This time you will get the error.

The encoding error comes from the fact that ‘texi->plain-text’ uses a
string port, and string ports internally use the current locale encoding
or ‘%default-port-encoding’.

Consequently, when running in the “C” locale, string ports cannot
represent non-ASCII code points (something widely regarded as a bug in
Guile, and at the very least an annoyance.)

To work around that, you can type this in *Guix Internal REPL*:

  (fluid-set! %default-port-encoding "UTF-8")

I fixed in commit 2cad18a8 of guix-artwork.git, but perhaps a similar
hack is apparently needed elsewhere.

Could you test this patch: