Gather your information. You need the title of the document, the Latin title, the source and the date it was published. Not all works have a Latin title so if you don't have one, don't worry about it.
Cite in-text by listing the title and chapter number in parentheses. You can choose to use the English or Latin title of the religious document. If you use the Latin title, put it in italics.
Cite the bibliography as English title, the Latin title (in italics), the source and the full date. For example: Decree on the Ministry and Life of Priests. Presbyterorum Ordinis. Vatican II, December 7th, 1965.
Note in the bibliography where you found the translation of any documents, as well. These documents are usually found in a book or online, which you would cite in standard MLA format.