You can suggest a better translation at https://crowdin.com/translate/inaturalistweb/38/en-fi#22334, and I’m happy to defer to the opinions of native speakers, though I’m guessing @mikkohei13 has an opinion.
FWIW, “naturalist” is a complicated word in English. If you’ll forgive the amateur / armchair history, in the 17th and 19th centuries it would have been considered synonymous with “scientist” and not had a particularly “professional” connotation. In the 20th century much of scientific interest become more specialized and codified into institutions, and the general study of natural phenomena perceivable to anyone came to be viewed by many as irrelevant or old fashioned. “Scientist” became an identity that suggested advanced levels of formal education and professional achievement marked by degrees, certifications, and other institutional markers, while “naturalist” became more associated with professional and volunteer educators who worked in parks and helped people understand the non-human world. My use of “naturalist” on iNaturalist intentionally attempts to dissolve those distinctions and assert a more wholistic identity defined as “someone with a conscious interest in non-human life” and includes university professors studying fly behavior, nature center employees teaching visitors about sea stars, and just anyone who’s ever stopped on the trail to wonder what a flower was, a bit more akin to the 19th century concept without the implication that the only people with the time and resources to pursue such interests are those unfairly benefitting from entrenched, systematic inequality (still true, alas, but perhaps less universal than it once was).
Which is a long way of saying that this one might be tough to translate.