The history of the Christian Church in the East has been one of virtually zero change, in terms of Theology and Churchmanship. The Greek Orthodox still use the Septuagint translation of the Old Testament, and a form of Greek for the New Testament, as well. Their Liturgy goes back to 4th or 5th Century. When the Orthodox Church occupied a new territory (which was rare, for they constantly faced first Persian, then Arab, then Turkish competition), though, they often allowed the local language to be used in lieu of Greek. One of the language provisions they made was for Latin, the language of Rome. Later, it would be argued that Rome didn’t have to ask to change the language; that the Bishop of Rome, and later the Patriarch, or Pope, was the designated follower of St. Peter, and as such was head of the whole Church. But, this claim was not made until late in the 500s, and not seriously entertained for another hundred years or more. The other Patriarchs, those of Jerusalem, Antioch, Alexandria and Constantinople pretty much ignored their brother in the west except for allowing that, since he really was in the line of Peter, he could be recognized as “first among equals” whenever they all met. Thus, when the Russians organized an Orthodox Church, Russian became the language of worship. The Serbs, too, organized their own Orthodox body, and they spoke (still do!) Serbian. The Jerusalem Church disappeared under the Arab onslaught, but the Antiochan Church spoke (and still worships in) Aramaic,, and the Alexandrian Church eventually adopted a modified Greek-Egyptian alphabet and language called “Coptic”, which today appears virtually nowhere except in Church Liturgy.
The Bishop of Rome, however, had different ideas about the Liturgy to be used in the West. Of the five Patriarchates, four were always entirely subject to the dictates of the Emperor, and thus never assumed any degree of temporal power, whatsoever. In Rome, the opposite was the case. In Rome, beginning in 410, the Pope became a secular, as well as religious, ruler, and very early on began making rules involving language, war, dress and taxes, and, as such, tried to create a firm hierarchy, not only of clergy, but also of secular rulers. The Popes of Rome wanted not only Deacons, Priests and Bishops to be subject to him, but also knights, princes and kings, as well. It was a very different dynamic from that of the Church in the East. The Popes also set Latin as the only language to be used in worship.
And, so, Latin, which had replaced Greek as the language of Christian worship in Italy and North Africa in the Fifth or Sixth Centuries was set to become the only approved language in the rest of the West, as well. This came as something of a shock in Ireland, Scotland and England, where Christianity preceded the establishment of the Roman Patriarchy, and to a lesser extent in Spain and France, in which there was also a preceding Christian tradition, the Gallican Church, which was also of pre-Roman provenance. By the sixth Century, too, Irish and Scottish missionaries were penetrating deep into the German lands of northern Europe, and the Popes wanted very much for those new Churches to be firmly under Roman control.