From CVS HEAD.
From addressbook/gui/widgets/e-addressbook-model.c lines 154 onwards:

static void
update_folder_bar_message (EABModel *model)
{
[...]
        switch (count) {
        case 0:
                message = g_strdup (_("No contacts"));
                break;
        case 1:
                message = g_strdup (_("1 contact"));
                break;
        default:
                message = g_strdup_printf (_("%d contacts"), count);
                break;
        }
[...]
}

This way of handling plurals is broken. Not all languages have only two
plural forms. In those languages, this is untranslatable. Please use
gettext's plural capability instead.

I don't think gettext plural handles case 0, but keeping that case separate
shpuldn't be a problem. But you should use gettext plural for all other
cases (1, 2, 3, ...).