There is a part in the Orthodox Divine Liturgy called the Dismissal of the Catechumens, in which the priest chants, "All ye catechumens, depart! Depart, ye catechumens! All ye that are catechumens, depart! Let no catechumens remain!" and this used to be important, because it would have been terrible for an outsider to see and misunderstand the meaning of the eucharist, when the early church was undergoing persecution. Now, the words remain, but it's understood that no one is expected to actually leave--it's just a tradition. However, some Orthodox churches today have problems with visitors leaving halfway through the service, not knowing that the Dismissal of the Catechumens is vestigial.
As Orthodox churches assimilate into American culture, the services shift from using the congregation's heart language to the English language, with some parts in one language, and some in the other. I've heard of a Romanian Orthodox church in DC that has its services entirely in English, except the Dismissal of the Catechumens is in Romanian, so no one leaves by mistake.