Client terminal, game service apparatus, and game service system and method thereof

A client terminal includes: a communication module for performing communication with a game service apparatus via a wired/wireless communication network; and a display unit for displaying a content of a message transmitted between a game user and a non-player character (NPC) during progress of an online game serviced by the game service apparatus. The terminal further includes a control unit for controlling so as to display the content of the message during progress of the online game, controlling so as to display a translated message of the content of the message provided from the game service apparatus upon a request of the game user, and transmitting modification data including edition data made by editing the translated message to the game service apparatus.