101 1. In accordance with the centuries-old tradition of the Latin rite, the Latin language is to be retained by clerics in the divine office. But in individual cases the ordinary has the power of granting the use of a vernacular translation to those clerics for whom the use of Latin constitutes a grave obstacle to their praying the office properly. The vernacular version, however, must be one that is drawn up according to the provision of Art. 36. 2. The competent superior has the power to grant the use of the vernacular in the celebration of the divine office, even in choir, to nuns and to members of institutes dedicated to acquiring perfection, both men who are not clerics and women. The version, however, must be one that is approved. 3. Any cleric bound to the divine office fulfills his obligation if he prays the office in the vernacular together with a group of the faithful or with those mentioned in 52 above provided that the text of the translation is approved.
Source: Sacrosanctum Concilium (Vatican.va)