It is very likely that Paul was drawing off of the Jewish religious custom and tradition (earliest “documentation” of this tradition may be found in Nehemiah 8 concerning ‘Ezra the Scribe’), whereby it was customary to have any readings, prayers, instruction, etc. given first in the Hebrew language, despite the fact virtually no one listening understood it. As soon as a few phrases were uttered, a reader standing next to the teacher would translate what was being said into the vernacular. This custom was carried to the early Christian church.
Maimonides, a renown 12th century Rabbi, scholar, and physician (considered one of the most influential and revered Jewish thinkers in the Middle Ages) also commented on this tradition. One if his comments is:
“From the time of Ezra, it was customary that a translator would translate to the people the [passages] read by the reader from the Torah, so that they would understand the subject matter. The office of the interpreter in Jewish liturgy.”
The Aramaic word for interpreter in the Talmud Megillah and commentaries associated with it is מתרגם meturgem in the singular and מתרגמין meturgemin in the plural. The plural is used more often.
In English this office is called the “meturgeman”. The interpreter had twofold usage as described by a Torah website:
"There were two types of Merturgemans (translators/interpreters). The first is the kind who stood by the Torah reader in the synagogue and translated into Aramaic as the reader read, verse by verse. It is mentioned dozens of times in the Talmud; once the Jews were exiled to Babylon, their vernacular was Aramaic – only the scholars and elders spoke or understood Hebrew. Thus, to make Torah reading understandable, it was translated.
In the same way, the Meturgeman would also sit by the Rabbi in the synagogue or the study hall. When the Rabbi would share words of Torah with the congregation or with his students, he would speak quietly in Hebrew and the translator would repeat his words in Aramaic."
Translating from one language to another, particularly the nuances of religious text and subject matter is no easy task. Indeed, Paul it’s very likely this concept is what Paul meant when he refers to the ‘gift of interpretation’.
The interpreter may not be the only individual in a given situation who knows the language of the speaker, but he’s typically the only one who has the ability to accurately translate what’s being said into the vernacular.
The point is in the first century Jewish world, religious service, readings, teaching, etc. particularly when done from a Temple (and especially from the Temple in Jerusalem), by historic custom and tradition were to be done *first* in Hebrew, then followed by translations into the vernacular – in short, Hebrew was the _expected language to be heard first_ . The apostles at Pentecost completely did away with this tradition and just began to speak to the crowd in the vernacular, dispensing with Hebrew altogether.