The first Christian Church was that of Jerusalem, Jewish.
Also recall at Pentecost, the apostles were speaking to many people in foreign tongue.
Many Christian Jews fled Israel during the Diaspora. The beginning communities of Roman Christians were Jewish who met in homes headed by presbyters.
Egypt, Syria, Palestine were teeming Christian populations. St. Mark founded the Church of Alexandria, Egypt. St. Peter the Church of Antioch. SS Peter and Paul the co founders of the Church of Rome. The Church of Constantinople emerged in Asia Minor after Christianity was almost decimated by Roman Emperors who moved their headquarters there due to barbarian invasions of Rome.
It is said St. James the Greater went to Spain but it was a failed mission…would like more (name removed by moderator)ut on his testimony of faith. St. Thomas went to India. All the apostles were sent but St. John the Evangelist wrote and died on the Island of Patmos.
The books of Scripture, the liturgy, the episcopal hierarchy of bishops, and foundations of the Creed were in place by 100 AD. You can look up St. Justin the Martyr who explained what happens at Mass to the Roman Emperor in 154 AD, and how the Mass was said throughout the entire Christian world at that time.