From my experience and my perspective, the translator knows everything without being an expert in all topics he/she translates. It is the duty of the translator to look for different topics that his/her clients propose him/her in each work.
I have to confess that acquiring new vocabulary, reading about the different topics to make a good translation, I’m passionate about it, since the translation’s jobs are as diverses as the clients.
We inform ourselves and we keep up to date when we’re looking for the terms more accurate to the document that’s going to be translated.
As Umberto Eco said, we try to say almost the same in the target language. And we also have to be at the forefront in orthographic rules, in syntax and grammar, to apply them properly in our work.
As you see, being translator is not just learning a second language, it is much more than that: studying constantly, reading and applying what you have learned.
And also I remember that before finding my vocation lin translation, many people told me: “translation is an easy field, the language is not as complex as exact sciences”. I can say with certainly: “translation is not so simple” “it has its complexity in its way” “the language can be as complex and a pain in the neck as exact sciences.