A data relay system for relaying data exchange between a server system of a service provider and a client system in accordance with the present invention comprises: a database section which is configured to store identification information for identifying language-dependent data and replacement data corresponding to the language-dependent data in association with each other; a server data receiving section which is configured to receive server data from the server system; a data processing section which is configured to detect the replacement data from the database section on the basis of the identification information contained in the server data; a data generating section which is configured to replace the language-dependent data as contained in the server data by the replacement data; and a client data transmitting section which is configured to transmit the server data as replaced to a client system.