A European scientist/natural philosopher in the 17th century (to just pick one) would have needed to know how to read and write Latin if they wanted to be part of a broader, international scientific community, yes. If they did not, they would be restricted to their local language. Sometimes that was enough — some areas (like France and Britain) developed robust-enough scientific communities that you could imagine "getting away" with being monoglot. But in other areas (like Russia) if you only spoke/write/read your native language you would be severely limiting your knowledge and your career.

An educated European in this time might learn several languages aside from Latin as a means of participating in the "republic of letters" — French, English, and Dutch were all valuable languages for science at this time. Did they all speak/write such languages? Of course not. There are certainly notable cases where translators were used (not "ghostwriters" — a ghostwriter is someone who does the actual work for you that you take credit for, a translator is just moving it from one language to another). A favorite example of mine is Marie-Anne Paulze Lavoisier, wife of Antoine Lavoisier, who acted as both a collaborator and translator. Lavosier had some classical languages, but not English, and in his field of study it was the work of an Englishman (Priestly) that was most relevant to him. She translated Priestly's works into English for her husband, and translated Lavosier's works into English for further publication.

So she not only translated things that were of use for him to do his work, she also wrote the translated editions of his own work.

Is that a normal case? Probably not — she was exceptional in many ways. But it does illustrate the language issues. These are not merely with Latin, as an aside. The "language of science" has changed over time (by Lavosier's time, it was French), sometimes being dominated by a single language (like Latin, or English today), sometimes being split into several languages (German, French, and English dominated much of the 19th and 20th centuries). Latin was only dominant for about three centuries (the 16th-19th, more or less) and even then there were plenty of non-Latin works of importance in science. There is a "folk history" of Latin dominance that sometimes clouds over the more complicated reality.

For waaaay more of this than you probably want, see Michael Gordin, Scientific Babel: How Science Was Done Before and After Global English (University of Chicago Press, 2015), esp. chapter 1, which is all about Latin.