"He will report himself" can be ambiguous, as either he can himself report, in person (which would be the correct meaning of this sentence, but the pronoun works intensively instead of reflexively, so can be left out), or he will report himself, such as for a misdemeanor crime, which would not be the verb "melden" (as far a I know).
technically, it's correct. it might indeed have the meaning of reporting oneself to the authorities as a self-denunciation. in a classroom it might also mean " to raise your finger in the air in order to indicate that you know the answer to the teacher's question or want to read out your homework".
but the main meaning of sich melden is get in touch, e.g. by means of a phone call, especially if it's a standalone phrase as shown above. so yes, i think it's an incorrect translation here.
Just a few sentences ago, I incorrectly answered this question as "He will announce himself." I accept that my answer was not very good. But Duo gave me as correct "He will report himself." So this time I gave exactly that translation, and this time that was wrong and it changed to "He will get in touch." This appears to be a programming error that happens quite frequently when my answer is not perfect. It isn't helping me learn. I wish Duo would give some attention to improving the program, rather than gimmicks and games. More focus on language accuracy would entice me to pay for the software.
It's sort-of meaningful.
It means something like "He will report...." But the thing which he will report is not mentioned, so it feels a bit incomplete to me in German. (Unlike English, where things such as "I don't know" or "He won't say" or "I can't tell" or "we will report on Sunday" or "they visited" are complete even without an explicit object.)
I wrote, "He will announce himself." Is this incorrect? I was thinking of a scenario in which a man is expected somewhere at an indefinite time and will notify the expecting party when he arrives; although, "He will announce his arrival" might be a better way to say that.
"He will come forward" wasn't accepted. Acceptable?
'2. etw., jmdn. bei einer Behörde, Stelle, Dienststelle nennen, angeben
e) ⟨sich für, zu etw. melden⟩ sich für, zu etw. bereit erklären
sich für eine Arbeit, Aufgabe melden
sich freiwillig melden
Beispiel von der Internet (Der Spiegel): Irak: Freiwillige melden sich bei Armee für Kampf gegen Isis Terror
come forward (TFD)
1. to offer one's services; volunteer
2. to present oneself