"You are getting sick."
Translation:Tu tombes malade.
No, "on" means an undefined group of people (even a group of one person could be defined by "on"), it can virtually replace any kind of personal pronoun (il/elle/tu/je/nous/vous/ils/elles). It's therefore very flexible when translating in English. Of course to know what it replaces we have to use the context.
- "Someone can tell me the first thing to do when we're late ?" = "Quelqu'un peut me dire la première chose à faire lorsqu'on est en retard ?"
- "Yes, me : when you are late, you should first apologize." = "Oui, moi : quand on est en retard, on doit d'abord s'exuser."
In this short discussion, people using "we" and "you" are not referring to actual persons, but are taking these pronouns as examples to be able to make their sentence. In French we can use "on" for that. But it's not necessarily the case we also can use "tu" or "vous" for this purpose, just like in English.
But you're right though, "on" progressively replaced "nous" (meaning actual persons) in common French.
- "Jean, Thomas, vous avez mangé ?" = "Jean, Thomas, did you eat ?"
- "Non, mais c'est bon on a pas faim." = "No, but that's ok we're fine."
In this example the "on" really means "we" as actual persons.
I hope I was clear enough.
I think you are confusing with something else. We would never use "faire malade" to mean "being sick" or "being ill". We would use "être malade" if the person is already sick, or "tomber malade" if the person just got sick.
Just as in English for "sick", "malade" in French can refer both to illness, evil doing or mental disorder. Just depends on the context.
However, we use "faire mal" to mean "doing harm" or "hurting". Maybe it's what confused you ?