The Language of the Hohoian King is a black magic skill used by Dark.
Dark learnt this skill after becoming closer to the Hohoian Gang. It allows him to communicate in the Hohoian language and motivate them.
When he gave the Hohoians orders in the Siege Round, the hohoians that were refusing to work became motivated to the max level and their gold collection rate increased by 200%.
Even the Hardcore Leveling Warrior who has seen a lot of skills was surprised to see such a skill.