Vatican website translation:
54. In Masses which are celebrated with the people, a suitable place may be allotted to their mother tongue. This is to apply in the first place to the readings and “the common prayer,” but also, as local conditions may warrant, to those parts which pertain to the people, according to the norm laid down in Art. 36 of this Constitution. Nevertheless steps should be taken so that the faithful may also be able to say or to sing together in Latin those parts of the Ordinary of the Mass which pertain to them. And wherever a more extended use of the mother tongue within the Mass appears desirable, the regulation laid down in Art. 40 of this Constitution is to be observed.
54. Linguae vernaculae in Missis cum populo celebratis congruus locus tribui possit, praesertim in lectionibus et “oratione communi”, ac, pro condicione locorum, etiam in partibus quae ad populum spectant, ad normam art. 36 huius Constitutionis. Provideatur tamen ut christifideles etiam lingua latina partes Ordinarii Missae quae ad ipsos spectant possint simul dicere vel cantare. Sicubi tamen amplior usus linguae vernaculae in Missa opportunus esse videatur, servetur praescriptum art. 40 huius Constitutionis.
Slavishly literal translation (kindness of Jonathan Day):
54. A suitable place may be allotted to the vernacular language in Masses that are celebrated with a congregation, especially in the readings and “the common prayer” and also, according to local agreement, in those parts which pertain to the people [‘look at’ the people], according to the norm in article 36 of this Constitution. It should, however, be arranged that the faithful may be able to say or sing together those parts of the Ordinary of the Mass that pertain to them, in the Latin language. Nevertheless if in any place a greater use of the vernacular language within the Mass seems desirable, the regulation in article 40 of this Constitution is to be followed.
The Council Fathers apply the general permission to employ the vernacular in Catholic worship found in article 36.2 to the particular case of the celebration of the Eucharist. There “readings and directives, … some … prayers and chants” are mentioned; here readings in the vernacular are reiterated and “the common prayer” (which had been restored in the preceding article) is also proposed to be prayed in the vernacular. Note that determining the extent of the use of the vernacular (as well as the translations to be employed) is the responsibility of the territorial bishops’ conferences with confirmation by the Apostolic See according to arts. 36.3 and 36.4. The final sentence of article 54 suggests that the Council Fathers foresaw situations in which territorial bishops’ conferences might request greater use of the vernacular than that listed in this article.
The Council Fathers also direct that worshipers should be prepared to say or chant the Latin texts of the Order Missae appropriate for assembly members, although they do not suggest the means by which this is to be done.
Pray, Tell readers may wish to discuss: 1) the wisdom of these directives in the light of fifty years’ experience; 2) how these directives have or have not been fulfilled and how that is to be interpreted (the “reception” of these directives); and/or 3) the practical processes by which the directives have been implemented.