8. A machine translation method, implemented using a computer, comprising: preparing 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, an interpretation word set element including the first expression, and a second expression element representing a second expression of a second language, wherein the first expression is to be translated into the second expression, and the first expression and the second expression are included in a category; acquiring, by the computer, a predetermined expression of the first language, the predetermined expression being included in a structure of a to-be-translated document, wherein words or sentences are arranged regularly in the structure; acquiring, by the computer, a first word set element including the predetermined expression and one or more expressions having equivalent positional relationship to the predetermined expression in the structure; detecting, by the computer, a subset from the plurality of interpretation data items, each of the subset including an expression element representing the predetermined expression and one or more word set elements; performing, by the computer, matching between the first word set element and each of the one or more word set elements of the detected subset based on at least one of a number and an order of expressions of the first word set element; selecting, by the computer, from the detected subset, an interpretation data item according to the matching; and translating, by the computer, the predetermined expression into the second language, using the selected interpretation data item.
8. A machine translation method, implemented using a computer, comprising: preparing 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, an interpretation word set element including the first expression, and a second expression element representing a second expression of a second language, wherein the first expression is to be translated into the second expression, and the first expression and the second expression are included in a category; acquiring, by the computer, a predetermined expression of the first language, the predetermined expression being included in a structure of a to-be-translated document, wherein words or sentences are arranged regularly in the structure; acquiring, by the computer, a first word set element including the predetermined expression and one or more expressions having equivalent positional relationship to the predetermined expression in the structure; detecting, by the computer, a subset from the plurality of interpretation data items, each of the subset including an expression element representing the predetermined expression and one or more word set elements; performing, by the computer, matching between the first word set element and each of the one or more word set elements of the detected subset based on at least one of a number and an order of expressions of the first word set element; selecting, by the computer, from the detected subset, an interpretation data item according to the matching; and translating, by the computer, the predetermined expression into the second language, using the selected interpretation data item. 9. The method according to claim 8 , wherein: the storage unit contains, as all or several of the plurality of interpretation data items, a condition used to select an interpretation data item including a word set element corresponding to the first word set element; and the method further includes selecting the interpretation data item including the word set element corresponding to the first word set element, if the detected subset contains the condition and the expression element representing the predetermined expression satisfies the condition.