Comment 9 for bug 1413226

here: http://bazaar.launchpad.net/~widelands-dev/widelands/trunk/view/head:/src/wui/attack_box.cc#L122

The update function:
m_text_soldiers->set_text((boost::format(_("%1% / %2%")) % m_slider_soldiers->get_value() % max_attackers).str());

The initialization:
sprintf(buf, "%u / %u", max_attackers > 0 ? 1 : 0, max_attackers);

Simply adding an underscore would create a new/different translation, so a replacement is needed (I do not know the difference/which one should be preferred).