Not true. And I would probably go as far as to say impossible. In my opinion, there are way too many languages for one person to know them all. Languages are like Pokémon, and I don’t know anyone who has caught them all. However, in opposing terms, I also feel that Linguists do not have to speak any other languages at all. To be a linguist would mean to study the background and history of languages and how they are used more so than just knowing how to speak one/any. But, in another definition, I suppose being a linguist could be one who speaks many languages.