Part III. The Liturgical Text
7. The language proper to the Roman Church is Latin. Hence it is forbidden to sing anything whatever in the vernacular in solemn liturgical functions-much more to sing in the vernacular the variable or common parts of the Mass and Office.
8. As the texts that may be rendered in music, and the order in which they are to be rendered, are determined for every liturgical function, it is not lawful to confuse this order or to change the prescribed texts for others selected at will, or to omit them either entirely or even in part, unless when the rubrics allow that some versicles of the text be supplied with the organ, while these versicles are simply recited in the choir. However, it is permissible, according to the custom of the Roman Church, to sing a motet to the Blessed Sacrament after the Benedictus in a solemn Mass. It is also permitted, after the Offertory prescribed for the mass has been sung, to execute during the time that remains a brief motet to words approved by the Church.
9. The liturgical text must be sung as it is in the books, without alteration or inversion of the words, without undue repetition, without breaking syllables, and always in a manner intelligible to the faithful who listen.