In describing the public Torah reading, the Mishna teaches that every person called to the Torah must read at least three pesukim, but that the turgeman (translator) should be given only one passage at a time to translate.
Although we are not familiar with the practice today, the turgeman was an essential fixture in the synagogue during Torah reading in the time of the Mishna and the Talmud, as well as for generations that followed. For Jews of Yemenite extraction, the turgeman is part of the standard Torah readings in their synagogues to this day. The job of the turgeman was to translate the Torah reading into a language that could be understood by all – Aramaic.
As can be well imagined, when the turgeman participated in the service, the Torah reading took a much longer amount of time. Although the Torah reading could not be shortened, when it came to reading the haftara – the portion from the Prophets that is read following the completion of the Torah reading – if there was a turgeman (and it should be noted that the Aramaic translation in Navi is even longer than in Humash, as it includes commentary alongside the literal translation), it made sense to shorten the reading. Thus, the original establishment of the haftara as consisting of minimally 21 pesukim (probably stemming from a desire to mimic the seven aliyot to the Torah, which are made up of three pesukim each) was cut down to ten pesukim, or even fewer.
There is another type of turgeman who is occasionally referred to in the Gemara; he is the individual whose job it was to “broadcast” the teachings of the Sage to the audience who came to hear him – an essential job prior to the invention of the loudspeaker. Such a turgeman not only presented the words of the Sage, but offered explanations and clarifications of the teachings, as well.