Apologies, seems I forgot to reply to all. See my message below.

Tl:dr: my OS had indeed a locale problem which I now corrected. Now it all
works well. Thanks for your help and sorry for the false report.

On Mon, Oct 11, 2021, 15:14 Darío Cuevas <superdarion@gmail.com> wrote:

> That was a quick reply.
>
> I checked and my locale was wrong (some values were set to "C",
> instead of the de_DE.UTF-8 of the rest), caused by some bad KDE plasma
> configuration file. It actually helped me solve an unrelated problem
> I've had for a while, so thanks a lot!
>
> Sorry to have reported it as a bug when it was my system's fault.
>
> Best regards,
> Darío
>
>
> El lun, 11 oct 2021 a las 14:14, Roman Perepelitsa
> (<roman.perepelitsa@gmail.com>) escribió:
> >
> > On Mon, 11 Oct 2021 at 14:05, Darío Cuevas <superdarion@gmail.com>
> wrote:
> >>
> >> To reproduce, one
> >> needs only do PROMPT="→" on .zshrc, open a terminal, start typing some
> >> command (e.g. ls) and hit TAB: the command (ls) will be written twice.
> >
> >
> > This usually happens when you put non-ascii characters in PROMPT (like
> that arrow) but your locale is not UTF-8. Run `locale` to confirm. To fix
> this, install and enable a UTF-8 locale.
> >
> > This can also happen when TERM environment variable doesn't match the
> real terminal type. To fix this you need to avoid overwriting the value of
> TERM set by the terminal.
> >
> > Roman.
>
>
>
> --
> Yes, indeed.
>