A system for identifying different language versions of the same structured format document (e.g., HTML web page) detects the language of the two documents and translates one or both into a preferred language if necessary, parses the two candidate documents and builds two hierarchical data structure based on the document. The data structures are used to compare the hierarchical structure of the two documents and also to access text portions in congruent positions in the two documents. A fuzzy measure of similarity of a set of text portions occupying congruent positions in the two documents is then obtained, to induce a measure of the similarity of the two documents which is compared to a fuzzy threshold.