Currently users can only interact with Darcs in English.  We should
(eventually) implement internationalization (i18n) and localization
(l10n) so that interact with Darcs in their native language.

I believe a de facto FOSS standard for this is GNU gettext, though I
don't know if it is available for Haskell yet.

http://en.wikipedia.org/wiki/GNU_gettext
http://www.gnu.org/software/gettext/gettext.html

Rationale (copied straight from gettext's homepage):

    Usually, programs are written and documented in English, and use
    English at execution time for interacting with users. [...] Using
    a common language is quite handy for communication between
    developers, maintainers and users from all countries. On the other
    hand, most people are less comfortable with English than with
    their own native language, and would rather be using their mother
    tongue for day to day's work, as far as possible. Many would
    simply love seeing their computer screen showing a lot less of
    English, and far more of their own language.

It seems that gettext is not yet available for Haskell:
http://www.mail-archive.com/haskell-cafe@haskell.org/msg45165.html

Besides the mentioned
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/i18n there is also
http://hackage.haskell.org/package/hgettext

If we adopt some i18n package, shouldn't we also start using some sort of error
code system for googleability? It would be a pity if you googled your error
message in Portuguese, you wouldn't find the helpful comments that people have
given in English.

BTW, I don't think this has a terribly high priority. Darcs is mostly used by
software developers, and whether it's good or bad, if you don't speak English
you're pretty lost as a software developer anyway. All the interesting books,
blogs and mailing lists about software are in English.