1. A machine translation system comprising: a storage unit configured to store a plurality of interpretation data items each including a first expression element representing a first expression of a first language, a word set element including the first expression, and a second expression element representing a second expression of a second language, the first expression being to be translated into the second expression, the first expression and the second expression belonging to a category; an acquiring unit configured to acquire a predetermined expression of the first language, the predetermined expression being contained in a to-be-translated text having a structure; a detecting unit configured to detect, from the interpretation data items, a plurality of interpretation data items each including an expression element representing the predetermined expression; a selection unit configured to select, from the detected interpretation data items, an interpretation data item including a word set element corresponding to a same attribute or an equivalent positional relationship in the structure; and a translation unit configured to translate the predetermined expression into the second language, using the selected interpretation data item.