Everyone knows that Quo Primum promulgated a revised edition of the Missale Romanum, and made it available to the whole Latin Church. Recent liturgical innovations were suppressed. The translation issue is about the conditions for a diocese or religious order to stop using their legitimate proper liturgical rite or usage (one more than 200 years old in 1570) and adopt the Roman Rite
The Latin says:
'nisi ab ipsa prima institutione a Sede Apostolica adprobata, vel consuetudine, quae, vel ipsa institutio super ducentos annos Missarum celebrandarum in eisdem Ecclesiis assidue observata sit: a quibus, ut praefatam celebrandi constitutionem vel consuetudinem nequaquam auferimus; sic si Missale hoc, quod nunc in lucem edi curavimus, iisdem magis placeret, de Episcopi, vel Praelati, Capitulique universi consensu, ut quibusvis non obstantibus, juxta illud Missas celebrare possint, permittimus;'
'saving only those in which the practice of saying Mass differently was granted over two hundred years ago simultaneously with the Apostolic See’s institution and confirmation of the church, and those in which there has prevailed a similar custom followed continuously for a period of not less than two hundred years; in which cases We in no wise rescind their prerogatives or customs aforesaid. Nevertheless, if this Missal which We have seen fit to publish be more agreeable to these last, We hereby permit them to celebrate Mass according to this rite, subject to the consent of their bishop or prelate, and of their whole Chapter, all else to the contrary notwithstanding.’
The more widespread translation has, instead of the emboldened words:
'provided they have the consent of their bishop or prelate or of their whole Chapter,'
But 'Capituli', '[consent] of the Chapter', has a '-que' stuck on the end (an 'enclitic'), which means 'and', just like the '-que' stuck on the end of 'filio' in the Creed ('filioque'). Just as the Holy Spirit proceeds from the Father and the Son, and not the Father OR the Son, so the consent is required of 'the bishop or prelate AND the Chapter', not 'OR the Chapter'.
In any case, the second translation would suggest a very puzzling provision, saying that the bishop could override the Chapter, or vice versa, but only in the direction of innovation, in adopting the Roman Rite. On the contrary, Pius V stacked all the cards in a conservative direction: a single dissenting canon in the cathedral chapter, or religious in an order's chapter, can prevent the loss of a venerable liturgical usage, and the superior and bishop also have a veto.
There is a widespread myth that Pius V and the Council of Trent in general imposed the Roman Rite on unwilling Catholics all over Europe, having first conducted a root-and-branch reform of it, comparable to the post Vatican II reform. This is complete tosh. The changes made to the new edition of the Missale Romanum in 1570, compared to the first printed edition in 1471, are extremely minor, and consist mostly of textual corrections in the light of manuscripts dating back no further than the 13th Century. This was imposed on no-one, to speak of: all the rites and usages we think of as important, historically, had a history going back much further than 200 years before Trent, and they happily continued in use afterwards. Gallican rites were still being used in France in the 19th Century; the Mozarabic Rite, the Ambrosian Rite, the usage of Braga, the usages of Dominicans, Premonstrensians, Carthusians and others carried on being used up to Vatican II, and many of them are still in use today.
Let's hope that the transparency of the web will allow accuracy to drive out error.