Your assumption is only true if the writer does not know the nuances of the languages that he is translating to and from.
For instance, in Isaiah 7:14, the LXX has the Hebrew word for “young girl” as “virgin.” The common thought is that the LXX were learned men in both Hebrew and Greek, and chose the best meaning for the translation to clearly show something uncommon would happen.
Your assumption is only true if the writer does not know the nuances of the languages that he is translating to and from.
When i was a kid the phrase (put a nickle in it and see if it will run) was used all of the time in the country but some one brought up in a college would not have any idea what it meant.
There has always been a gap in communication between the educated and the uneducated but it used to be much worse.
Also I am told that the new testament was written in Greek so they would have no Hebrew or Aramaic to translate it from but only descriptions of the events from memories of people who were witnesses.