Tosefta su Esodo 7:30

One person [publicly] reads the [weekly portion of the] Torah and one translates. There should not be one who reads and two who translate, and not two who read and one who translates, and not two who read and two who translate. One person reads the Prophets (i.e., the haftarah) and one translates, [or] one reads and two translate, but there should not be two who read and one who translates, and not two who read and two who translate. One person reads the Megillah and one translates, [or] one reads and two translate, [or] two read and one translates, [or] two read and two translate. A minor [may] translate under the supervision of an adult, but it is undignified for an adult to translate under the supervision of a minor, as it says (Ex. 7:2), "And Aaron your brother will be a prophet to you." The prayer-leader of the congregation shall not [lead the] prayers until others urge him to do so, and even the head of the congregation shall not [lead the] prayers until others urge him to do so, as no one should take something for himself (i.e., the performance of a mitzvah to which others may be entitled, see Minchat Bikkurim here) with his own hands.

One person [publicly] reads the [weekly portion of the] Torah and one translates. There should not be one who reads and two who translate, and not two who read and one who translates, and not two who read and two who translate. One person reads the Prophets (i.e., the haftarah) and one translates, [or] one reads and two translate, but there should not be two who read and one who translates, and not two who read and two who translate. One person reads the Megillah and one translates, [or] one reads and two translate, [or] two read and one translates, [or] two read and two translate. A minor [may] translate under the supervision of an adult, but it is undignified for an adult to translate under the supervision of a minor, as it says (Ex. 7:2), "And Aaron your brother will be a prophet to you." The prayer-leader of the congregation shall not [lead the] prayers until others urge him to do so, and even the head of the congregation shall not [lead the] prayers until others urge him to do so, as no one should take something for himself (i.e., the performance of a mitzvah to which others may be entitled, see Minchat Bikkurim here) with his own hands.