As established in the Real Academia Española, Spanish-speaking countries use, generally, the ascending order when they write out dates, i.e. day, month, year, with no commas separating any information: 31 de diciembre de 1992. Between the day and the month, as well as between the month and the year, the preposition “de” is used. For purposes of uniformity, it is recommended to use that structure for all countries whose official language is Spanish.
In Spanish texts written in English-speaking countries, it is common to find the structure month, day, year: diciembre 31 de 1992. No preposition is used between month and day. Though this model is used in certain parts of Latin America, it is not recommended for Spanish texts due to the influence of English.
ISO standards recommend a descending order, meaning year, month, day, with no preposition between the elements: 1992 diciembre 31. This model is used in scientific and technical documents that are published for international audiences.