Now that the dust is settling, after the publication of the Motu Proprio Summorum Pontificum, two serious errors in the English translation provided by the Vatican have been revealed.
Careless and tendentious translation at the Vatican is been an extremely serious problem, chronicled in detail by the famous blogger Fr Z. In the case of the MP, no 'official' translation has been provided, but the Vatican's 'unofficial' translation, from the Vatican Information Service, has naturally been the basis of commentary, and of the 'guidance' being offered by various bishops around the world. This can lead to errors, and of course even when an official translation appears, the Latin is the normative text, not the English or any other translation.
The two problems are these.
Article 5 secton 1: In paraoeciis, ubi coetus fidelium traditioni liturgicae antecedenti adherentium continenter exsistit, parochus eorum petitiones as celebrandum santam Missam iuxta ritum Missalis Romani anno 1962 editi, libenter suscipiat.
The Vatican translation: In parishes, where there is a stable group of faithful who adhere to the earlier liturgical tradition, the pastor should willingly accept their requests to celebrate the Mass according to the rite of the Roman Missal published in 1962...
The problem here is the phrase 'stable group of faithful'. The 'coetus fidelium' is to be 'continenter exsistet' - continuously present, ie not just passing through. (A separate article deals with the right of people passing through to the Traditional Mass: for funerals, pilgrimages etc..) Fr Z makes this point here: the word 'continenter' does not imply that the group must be of any particular size; a 'coetus' can be three people, including the priest, and it is this which would justify a pastor celebrating the Traditional Mass publicly.
Article 5, section 4: Sacerdotes Missali B. Ioannis XXIII utentes, idonei esse debent ac iure non impediti.
The Vatican translation: Priests who use the Missal of Blessed John XXIII must be qualified to do so and not juridically impeded.
The problem here is the word 'idoneus' implies only legal, rather than academic or intellectual, qualification. Just as a newly elected religious superior must be 'idoneus' to take up his or her position, so must a priest who is to say the Traditional Mass. While it would certainly not be fitting for a priest to say the Mass without proper preparation, and without knowing what he was doing, the Holy Father is not imposing a requirement for any formal qualifications (passing Latin exams etc.) by using the word 'idoneus'. Fr Z makes that point here.
The difficulty of translating 'idoneus' neatly has led Rorate Caeli, who adapted the English translation for its readers, to render the phrase simply 'must be idoneus'. Unfortunately, even their translation misses the first problem discussed above. Nevertheless, it is recommended because it puts the Latin and English in parallel columns.