Fr. John Zuhlsdorf has a bit of context on the mandate from the Congregation for Divine Worship that "pro multis" in the Eucharistic Prayers be translated as "for many" not as "for all."

(it is translated as "for all" in the German, Spanish and French translations, according to Fr. Z – but not in the French – pour la multitude.)

This seems like a minor matter, but believe it or not, it has been one of the most contentious liturgical disputes of recent decades.  In fact, some radical traditionalists have proclaimed that the translation of the words as "for all" invalidated the entire Mass, etc.

To quote from Cardinal Arinze’s letter on the subject:

The Synoptic Gospels (Mt 26,28; Mk 14,24) make specific reference to “many” for whom the Lord is offering the Sacrifice, and this wording has been emphasized by some biblical scholars in connection with the words of the prophet Isaiah (53, 11-12). It would have been entirely possible in the Gospel texts to have said “for all” (for example, cf. Luke 12,41); instead, the formula given in the institution narrative is “for many”, and the words have been faithfully translated thus in most modern biblical versions.

The Roman Rite in Latin has always said pro multis and never pro omnibus in the consecration of the chalice.

The anaphoras of the various Oriental Rites, whether in Greek, Syriac, Armenian, the Slavic languages, etc., contain the verbal equivalent of the Latin pro multis in their respective languages.

“For many” is a faithful translation of pro multis, whereas “for all” is rather an explanation of the sort that belongs properly to catechesis.

The expression “for many”, while remaining open to the inclusion of each human person, is reflective also of the fact that this salvation is not brought about in some mechanistic way, without one’s willing or participation; rather, the believer is invited to accept in faith the gift that is being offered and to receive the supernatural life that is given to those who participate in this mystery, living it out in their lives as well so as to be numbered among the “many” to whom the text refers.

Here is a link to 4 article Fr. Z has written on the translation of these words, in case you’re interested in learning more.

The entire letter, dated 10/17, is here.