"He is probably healthy again."
Translation:Er dürfte wieder gesund sein.
Looks like "He may be healthy again" = "He is probably healthy again"
Yeah, in german it is like this. Er ist wahrscheinlich wieder gesund and er dürfte wieder gesund sein. Both describe the same thing.
Yes, it's the same literal phrasing; but the meaning is closer to "He ought to be healthy again". It's more certain than "He may be healthy again".
Interesting usage of the modal verb dürfen! Look on this page under "Special Meanings" for more information: http://www.dartmouth.edu/~deutsch/Grammatik/Verbs/modals.html
I think "wohl" is closer to "apparently" in this context, it sounds like you've heard it say, or you've received some hint (e.g. you've seen him running in the park, you've seen your colleague in your office building): "I gather / It seems like he's healthy again".
If you just think that "his cold ought to be gone after these four weeks" (and he hasn't said anything about his health since then), "wohl" doesn't really work.
...except if you use Konjunktiv like in Duolingo's sentence: "Er dürfte wohl wieder gesund sein" - but then "wohl" is really just a filler word. It can add a more speculative tone, but it could be used just for emphasis as well ("Of course he'll be able to join us; after four weeks he should be healthy again, shouldn't he?").
"Nach vier Wochen / Bis dahin ist er ja wohl wieder gesund!" would work, too, if you want to brush of the ridiculous suggestion that he might still be too ill to join you (after four weeks of alleged illness / at the event in the future). So this is along the lines of "he's bound to be healthy again".
"wohl" can mean "probably" as well, though, e.g. in "Where are you spending your holidays?" - "Ich fahre wohl nach Spanien."
Edit: ...so, basically, I think "wohl" and the "er dürfte..." construction often (!) don't significantly differ in meaning and connotation, but as a translation of "probably", I think "er dürfte..." works better, because in English there are phrases that translate "wohl" much more accurately than "probably", in most contexts, as far as I can see.
... I now understand less how wohl is used (as in, I am a lot more confused than before), but I appreciate your effort regardless.
Well, "wahrscheinlich" would be the literal translation of "probably", but I think "vermutlich" works as well.
Just take into account that "vermutlich" implies that someone (the speaker, or somebody whose opinion the speaker is "quoting") supposes (or assumes or guesses) that he is healthy again. That doesn't necessarily correlate with the probability of him being healthy again.