From the 2001 Instruction Liturgiam Authenticam, at vatican.va/roman_curia/congregations/ccdds/documents/rc_con_ccdds_doc_20010507_liturgiam-authenticam_en.html :
“83. As regards the editions of liturgical books prepared in vernacular languages, the approbation of the Conference of Bishops as well as the recognitio of the Apostolic See are to be regarded as valid only for the territory of the same Conference, so that these editions may not be used in another territory without the consent of the Apostolic See, except in those particular circumstances mentioned above, in nn. 18 and 76, and in keeping with the norms set forth there.”
“18. In celebrations for speakers of a foreign language, such as visitors, migrants, pilgrims, etc., it is permissible, with the consent of the diocesan Bishop, to celebrate the Sacred Liturgy in a vernacular language known to these people, using a liturgical book already approved by the competent authority with the subsequent recognitio of the Apostolic See. If such celebrations recur with some frequency, the diocesan Bishop is to send a brief report to the Congregation for Divine Worship and the Discipline of the Sacraments, describing the circumstances, the number of participants, and the editions used.”
Here are some problems I see with a United Kingdom Priest using a United State’s Liturgy of the Hours in private:
- The priest will not become familiar with the books that he will use in public ceremonies.
- He will not using the same books, the same translation of the psalms, as the priests and religious in his area.
- This will influence things like his preparation of homilies, his discussions with others about the psalms, etc.
- As a seminarian the UK books would be used in ceremonies in the seminary.