Saint Brendan really makes it to America and lands in Yucatan. With the permission of a local ruler he and the other monks found a monestary and are finally successful in converting the local ruler's successor to christianity. This ruler turns into a mesoamerican Charlemagne and conquers at first other mayan city states and finally even Teotihuacan, where he sets up his new capital. When the question of a common admistrative language for the new empire comes up, Saint Brandan's successor proposes Latin, because it is not only neutral and has a fully developped script, it is the liturgic language of the new empire's state religion as well.
Since especially monastic christianity is a rather peaceful religion when compared to the different mesoamerican cults demanding human sacrifices it is readily accepted by the conquered peoples, and while some syncretism is inevitable, it is accepted by Saint Brendan's successors for the greater good of the conversion effort.
When the first Europeans arrive in the Americas nearly a thousand years later they discover a christian society speaking a romanised Nahuan, written in the irish version of Latin script and practicing a form of christianity, that, while different from both Catholic and Orthodox, is still recognisable. Since they expect to have landed in India they of course assume to have found the empire of Prester John, which they do not conquer but only trade with.
Since especially monastic christianity is a rather peaceful religion when compared to the different mesoamerican cults demanding human sacrifices it is readily accepted by the conquered peoples, and while some syncretism is inevitable, it is accepted by Saint Brendan's successors for the greater good of the conversion effort.
When the first Europeans arrive in the Americas nearly a thousand years later they discover a christian society speaking a romanised Nahuan, written in the irish version of Latin script and practicing a form of christianity, that, while different from both Catholic and Orthodox, is still recognisable. Since they expect to have landed in India they of course assume to have found the empire of Prester John, which they do not conquer but only trade with.