FYI, the text you quoted is from VII, not Trent. And it’s not 'Particular Law" which is a specific Canonical term. It is Universal Law of the Latin Rite.
As I posted it is from Vatican II* Constitution on the Liturgy * # 36 (1)
The use of the Latin language, with due respect to
particular law, is to be preserved in the Latin rites
This “law” comes from Canon 9 Council of Trent,
*Session XXII Doctrine Concerning The Sacrifice Of The Mass *
Canon 6. If anyone says that the canon of the mass contains errors and is therefore to be abrogated,[25] let him be anathema.
Canon 7. If anyone says that the ceremonies, vestments, and outward signs which the Catholic Church uses in the celebration of masses, are incentives to impiety rather than stimulants to piety,[26] let him be anathema.
Canon 8. If anyone says that masses in which the priest alone communicates sacramentally are illicit and are therefore to be abrogated,[27] let him be anathema.
Canon 9. If anyone says that the rite of the Roman Church, according to which a part of the canon and the words of consecration are pronounced in a low tone, is to be condemned; or that the mass ought to be celebrated in the vernacular tongue only;[28] or that water ought not to be mixed with the wine that is to be offered in the chalice because it is contrary to the institution of Christ,[29] let him be anathema.
Even the theologians of the Consilium recognized this law
“ Some would have preferred to see the rite completely revised. The Consilium was of this opinion from the beginning, and it had even prepared a draft…. But the resultant Mass, partly in Latin, partly in the vernacular, was a hybrid, lacking in continuity… **the vernaculars had to stop at the threshold of the Roman Canon…**
Reform of the Liturgy-Annabale Bugnini
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