Q. I hear that our ancestors translated the Torah reading as they went. Why don’t we do the same?
According to Rav (Meg. 3a), this practice dates from the time of Ezra, from 444 BCE, when the public reading of the Torah was carried out m’forash – “distinctly” (Neh. 8:8), which Rav understands as targum, “with translation”.
As late as the time of Natan HaBavli, 9th cent., there was still a public translation into Aramaic with the Exilarch (political head of Babylonian Jewry) called up to read the Torah and the Gaon of Sura called to translate. The translation of the Torah was done verse by verse and of the haftarah, every three verses.
The m’turgeman (translator) was not allowed to use a book or look into the Hebrew text (as opposed to the Torah reader himself, who was not allowed not to look at the text) so that no-one would think his version was actually in the Torah itself and therefore authoritative and immutable.
These days an Aramaic translation would make sense to very few people. Other languages would be more relevant. But our current usage is to have good translations available in printed form and members of a congregation are encouraged to follow the reading by this means.