Translation is sometimes treated as loss. The Targum tradition says something braver: if the people no longer understand, the Torah must still be heard. Meaning has to cross the room.
Onkelos became the disciplined version of that crossing. Hebrew remained the text. Aramaic became the public bridge, close enough to serve and careful enough not to replace.
The record
Targum Onkelos is the standard Aramaic translation of the Torah in rabbinic Jewish tradition.
The practice of rendering biblical readings into Aramaic reflects a world in which many Jews spoke or understood Aramaic more readily than biblical Hebrew.
When Hebrew grew strange to many listeners, the synagogue read on in Aramaic, the language of the street.
The record
Rabbinic sources discuss the public reading of Torah together with translation, preserving both Hebrew text and vernacular explanation.