Here I think there is a misrepresentation of what the role of the Papacy is in the Church. While the Pope is the Vicar of Christ, and the Supreme Head of the Church on Earth, he does not spend his day making infallible pronouncements on Scripture or any other issues. He does guide, teach and govern the Church, by virtue of the Authority given to Peter and his successors by Christ.
As far as his other obligations they are to be guardian of the Sacred Deposit of the Faith, which includes the Sacred Scriptures. As far as defining the Sacred Scriptures, the quote you provided from the CCC is a good start. But as has been brought up before, the CCC or any approved Catechism is not the full extent of Catholic Teaching. While all Catechisms are composed of both Doctrine, and Disciplines of the Church. An example of each would be (Doctrine) There is one God, in Three Persons. As to the latter, the custom of using Holy Water to bless oneself may be included in one Catechism, but omitted by another author in his or her catechism. Since the Catechism is not the final autority on all aspects of a subject, but a shortened guide to the Faith, one cannot stop where the Catechism stops, but will hopefully grow in Faith beyond the limits of the Catechism.
The quote you provided mentions the Magesterium, which is not just the Pope, but the Teaching Authority of the Church, which includes bishops, priests, anyone appointed to teach on behalf of the Local Bishop, who is by proxy teaching in union with the Pope. The Pope also must submit, to the Sacred Scriptures, and Sacred Tradition, and does not have the authority, as some think to change either, but the obligation to guard what has been passed on to him. This includes, when questions arise as to proper interpretation further explanation of the proper application of these sources. We look to the writings of the Fathers, as well as other sources for interpreting the Scriptures. Teaching and Interpreting the Sacred Scriptures within the Catholic Church does very much include the understanding of the the Linguistic and Cultural Norms at the time the individual books were written. Even before Dr. Luther and the beginnings of Protestantims, Catholic Biblical Scholars studied the ancient text in the context of the language and customs of the time. St. Jerome in an effort to translate the Vulgate even learned Hebrew from the Rabbis in Isreal, and delved into the Meanings of both the different versions of the Hebrew Scriptures and the LXX in determining the best sources and most authentic translation. While the Vulgate is looked to as the Primary and Official text of the Scriptures, there are any number of versions that are used in Scripture study. Prior to Dr. Luther there were a number of translations in both High and Low German, that the Catholic Church approved for reading by German Speaking countries, as well as dozens of French, Italian, a Bohemian, Slavonik, and Spanish versions that had the approbation of the Church. The main issue that prevented them from becoming widespread was the general illiteracy of the people, (one of the reasons for the artwork in the major churches and cathedrals in Europe also known as “The People’s Bible”) and Guettenberg’s invention of movable type had yet to be invented.
I know I’m wandering all over the map, however I do want to stress that the CCC, while a good synopsis of the Faith, is simply a starting point, and not the entire faith. And the role of the Pope in the day to day workings of the Church is often overemphasised in some Protestant circles, who try to support an error that Catholics do not have the right or ability to think for themselves, but must submit each and every thought to the Pope for approval.