Okay, that's kind of confusing... "worker" seems to behave like an adjective... Is this how it works ? Do they use the same word for "a hard-working person" and "a worker" ? Because we do that in french too and I think it kind of makes sense, but I need a confirmation please !
You are partially correct. "Рабочий" does work both as an adjective and a noun, but the meaning of the adjective "рабочий" is not "hard-working" but rather "working" in a sense of "operational", "functional". As for the "hard'working person", no, "рабочий" is not used for that meaning.
The only time I can remember hearing the word laborer in American English is in the 1985 movie Real Genius when he says "You're laborers you're supposed to be laboring. That's what you get for not having an education." I'd say it's an extremely rare word in English and probably "worker" is a better translation.