The general guideline of the Orthodox Church has always been to allow believers to worship, read and pray in the language which they understand.
In his Ecclesiastical History, Theodoret describes how, in the 4th century, John Chrysostom ministered to the Goths (Scythians) within Greek-speaking Constantinople itself:
Appointing presbyters and deacons and readers of the divine oracles
who spoke the Scythian tongue, he assigned a church to them, and by
their means won many from their error. He used frequently himself to
visit it and preach there, using an interpreter who was skilled in
both languages, and he got other good speakers to do the same. This
was his constant practice in the city, and many of those who had been
deceived he rescued by pointing out to them the truth of the apostolic
Book V, Chapter XXX
The existence of the Cyrillic alphabet provides another such example of such support. The Prologue describes how Cyril and Methodius ministered to the Slavs:
When the Khazarite king, Kagan, sought preachers of the Christian
faith from the Emperor Michael, the Emperor commanded that these two
brothers be found and sent to the Khazars. They converted Kagan to the
Christian faith and baptised him, together with a great number of his
nobles and an even greater number of the people. After some time, they
returned to Constantinople, where they compiled a Slavic alphabet of
38 letters and began to translate the service books from Greek into
Slavonic. At the invitation of Prince Rastislav, they went to Moravia,
where, with great devotion, they spread and confirmed the Faith, made
more copies of the books, brought them priests and taught the young.
Lives of Sts. Cyril and Methodius
Today the Orthodox Church comprises four of the five ancient Patriarchates (Constantinople, Alexandria, Antioch, Jerusalem), nine autocephalous Churches (ten if the Orthodox Church in America is counted), and five autonomous Churches (Kallistos Ware, The Orthodox Church, pp. 5-6). These Churches not only support worship in the local language, but also - in the spirit of John Chrysostom - often in the language of any foreigners who happen to be present. In the Cathedral of St. Luke in Hong Kong, which belongs to the Patriarchate of Constantinople, for example, I have heard English, Cantonese, Greek, Romanian, Russian, and French all used in the same service, depending on who happened to be visiting that particular Sunday.
Although the Jesus Prayer is understood to be mystical by Orthodox believers, it is not "magical". It is a prayer and not an incantation and, as such, falls entirely within the Orthodox tradition of prayer and worship in one's own language.