1. A system for translating messages, the system comprising: a message storage unit for storing a first message, a second message, and a third message, wherein the same content is respectively described in the first message and the second message in a first language and a second language that are different from each other; a parsing unit for generating a first syntactic tree that represents a hierarchical structure of words and phrases included in the first message and a second syntactic tree that represents a hierarchical structure of words and phrases included in the second message by an operation of a CPU, by reading the first and second messages from the message storage unit and parsing the first and second messages; a determining unit for determining, the operation of the CPU, whether a representation of a phrase represented by a certain subtree included in the first syntactic tree matches a representation of a phrase represented by a subtree, corresponding to the certain subtree, in the second syntactic tree, and, on the condition that the representations match each other, determining that the phrase is a phrase that need not be translated; and a translation unit for outputting, in a process of generating a fourth message described in a fourth language by translating a third message described in a third language by the operation of the CPU, the phrase that need not be translated and is included in the third message, as represented in the third message, the phrase being put in the fourth message after the translation.