Historically what percentage of the Catholic Church's liturgical function was done in Latin?

Historically what percentage of the Catholic Church's liturgical function was done in Latin?

It seems logical to assert that the majority of the Roman Rite Masses were entirely in Latin, except for the sermons which would naturally be in the vernacular. Even this was sometimes done in Latin, especially in universities or where the majority of the mass attendees understood Latin.

Historically, some papal Masses and funerals of Roman Cardinals the Gospel would be chanted in Greek as a sign of the universality of the Catholic Church. See this article: The Greek Deacon of the Papal Rite of Mass.

St. Francis de Sales preached eloquent sermons in French around the time of Protestant Revolution. Missionaries would have a hard time making converts if the sermons at mass were habitually in Latin.

Another example is that of Abbot Aelfric:

In the final decade before the year 1000, an Anglo-Saxon abbot named Aelfric wrote and distributed three series of homilies in the Old English language, all, or nearly all, of which have survived. David Knowles, in his monumental volume, The Monastic Order in England, describes Aelfric’s place in early English church history as “second only to Bede and in direct spiritual descent from him.” Aelfric appears to clearly state his purpose for the composition of his homilies in two prefaces attached to the first series of forty homilies, with the first preface written in Latin and the second in Old English. These homilies, he states, have been compiled and translated from the works of church fathers such as Augustine, Jerome, and Bede, and are to be read by priests in English churches to the unlearned, who cannot understand the Latin of the Scriptures and liturgy, but only their own native tongue. - [“In the Language to which They Were Born”: A Study of Audience for the Vernacular Catholic Homilies of Aelfric](“In the Language to which They Were Born”: A Study of Audience for the Vernacular Catholic Homilies of Aelfric)

Hymns and other pieces of sung liturgical songs or psalms were uniquely Latin in Latin Masses of the Roman Rite. In fact the vernacular practice of doing such creeped in after the Protestant Revolution.

Singing in the vernacular may not be substituted for the latter. This abuse crept in after the Reformation, and flourished in the eighteenth century, particularly in Germany and adjacent countries. The wish of the Church is that this abuse should be everywhere extirpated, while violence to local customs be avoided. - Singing by the people

This said, not all Masses in the Roman Rite were in Latin.

Although Latin prevails in the West as a unified liturgical language, in the face of certain circumstances the Roman church has made exceptions to provide a language in the Liturgy more familiar to the people. It is in the ninth century among the Slavic nations that we find a departure from liturgical Latin in divine worship. A privilege was first granted to Sts. Cyril and Methodius, by Pope Hadrian II in 869, and again by Pope John VIII in 880 to use the vernacular (Slavonic) in the Liturgy.

Another example of the flexibility of which the Roman rite is capable is the privilege granted for the use of Chinese as a liturgical language. History records in the fourteenth century that the first Franciscan missionary to China, John of Monte Corvino, used the vernacular in the Liturgy.26 Pope Paul V, in a brief of June 27, 1615, granted the same privilege to Jesuit missionaries. As recently as 1949, the privilege to use the Chinese literary language in the Liturgy was granted by the Holy Office.

Still further concessions have been granted:

a) During the fourteenth century the Roman Liturgy in its Dominican variant was translated into Greek for use by the Dominican missionaries in Greece.

b) Permission had been granted to celebrate the Dominican Liturgy in the Armenian classical language in Armenia.

c) At the end of the sixteenth century missionaries of India of the Latin rite were allowed to celebrate Mass in Syriac.

I) In 1959, the Holy See renewed Germany's privilege to use the vernacular (German) in the Epistle and Gospel after they are recited in Latin. - Liturgical Languages

In other words, the exact same Mass could be said in at least three languages: Latin, Greek and Old Slavonic and thus were considered Roman Catholic and not Eastern Rite Catholics. Please note that some authors employ the term Greek Rite or Old Slavonic Rite, but in this case, the term means a variation or usage of the Roman Rite.

The Roman Rite is used in Dalmatia in an Old Slavonic version (written in Glagolitic letters), occasionally in Greek in Italy; but in any language it is always the Roman Rite. - Catholic Encyclopedia

The Holy Sacrifice of the Mass: Dogmatically, Liturgically and Ascetically Explained (1902) by Fr. Nikolaus Gihr writes in the first footnote of §32, "The Language Used in the Celebration of the Holy Mass" (p. 319-328):

Whether the Apostles celebrated the Holy Sacrifice in the language of each individual nation or only in the Aramean (Syro-Chaldaic), Greek and Latin languages cannot be determined with certainty. In any case, from the first four centuries no liturgy can be shown composed in any other than the three languages of the inscription of the Cross [i.e., Hebrew, Greek, Latin]. In the West, for example, in Italy, in Germany, in Spain, in France, in England, Latin was at all times the liturgical language. Toward the end of the ninth century Pope John VIII. (872-882) permitted the Moravian Slavs, converted by Sts. Cyril and Methodius, to celebrate the liturgy in their (Slavonic or Glagolitic) native language, and that probably in order to prevent their apostasy to the Greek Schism. In the East also the Church later on permitted some schismatics and heretics, who had returned to the unity of the Church (for instance, the Copts, Armenians, Ethiopians), to retain their native language in the liturgy.

Fr. Adrian Fortescue's 1917 The Mass: A Study in the Roman Liturgy says, in §3 "Latin as a Liturgical Language" of the ch. "The Origin of the Roman Rite," that (p. 126-127):

Latin was apparently first used by Christians in Africa. Pope Victor I (190-202), who was an African, is generally quoted as the first Roman to use it.³ Novatian (c. 251) writes in Latin; since about the third century this becomes the usual and then the only language spoken by Christians at Rome. When it replaced Greek in Church is disputed. Kattenbusch dates it as the liturgical the second half of the third century,⁴ Watterich,⁵ Probst⁶ and Rietschel⁷ think that Greek was used till the end of the fourth century. In any case the process was a gradual one. Both languages must have beenused side by side during a fairly long period of transition. A certain Marius Victorinus Africanus, writin about 360 in Latin, still quotes a liturgical prayer in Greek.¹ The Bible existed only in the Greek Septuagint for some time.² The lessons were read in Greek at Rome, at any rate on some days, till the VIIIth century;³ some psalms were sung in Greek at the same time.⁴ Amalarius of Metz⁵ († c. 857) and Pseudo-Alcuin⁶ still mention Greek forms. The creed at baptism may be said in either Greek or Latin, at the convert's discretion, according to the Gelasian Sacramentary.⁷ But our present Greek fragments⁸ are later interpolations.

By at least the 12^th century, the Latin language in the Roman (i.e., Latin) Rite was most widely used, and, as Fr. Gihr writes (p. 319-320), it was attacked by heretics and schismatics:

The Mass considered in itself could assuredly be celebrated in any language, but by the Providence of God the Latin language has become, and still continues to be of all languages the most widely diffused for divine worship.² The very ancient practice of the Church of celebrating Mass in the West, not in the living language of the country, but in a dead language, that is, in Latin, for the most part a language unintelligible to the people, has since the twelfth century to the present epoch been frequently made the subject of attack.

Between the 12th century and the Council of Trent, there were some oddities or abuses like half-Latin, half-vernacular sequences (cf. Fortescue p. 275), but the Council of Trent curtailed these by saying (Session 22, can. 9):

Canon IX.—If anyone saith, … that the mass ought to be celebrated in the vulgar tongue only… let him be anathema.

Regarding homilies: These are meant for the instruction of the faithful, and thus they were in the vernacular.

For the most recent scholarship on this topic, see:

• Reid, Alcuin. The Organic Development of the Liturgy: The Principles of Liturgical Reform and Their Relation to the Twentieth Century Liturgical Movement prior to the Second Vatican Council (Farnborough, Hants.: St. Michael’s Abbey Press, 2004).

International Federation Una Voce (FIUV)'s position paper:

• PP 7: Latin as Liturgical Language (revised 10/10/12)

FIUV is an international organization promoting the pre-Vatican II Roman Rite Mass in Latin.