It seems like gettext only searches for locale information in /usr/share/locale, by default. I installed ikiwiki into /usr/local, therefore the locale information wasn't found. This patch fixes the issue:

    --- a/IkiWiki.pm
    +++ b/IkiWiki.pm
    @@ -1057,6 +1057,7 @@ sub gettext { #{{{
                                    $gettext_obj=undef;
                                    return shift;
                            }
    +                       $gettext_obj->dir("$installdir/share/locale/");
                    }
                    return $gettext_obj->get(shift);
            }

[[tag patch]]
-- [[ThomasBleher]]