Good morning, both are correct, but mean different things.
1) A translator TOLD the President what everyone was saying. This is a simple past tense form indicating a completed action. Think of this as a *photo* from yesterday of a translator talking to the president.
2) A translator WAS TELLING the President what everyone was saying. This is past progressive, meaning the action is in the past, but it is ongoing in the past. The action of telling is ongoing and has not finished. Think of this as a *video* from yesterday of the translator talking to the president.
I hope this helps.