If you open any German textbook about German grammar, you will find description of these four types of objects in german sentences:
Das Buch gehört dem Mann.
Das Kind sieht den Mann.
Die Angehörigen gedenken des Mannes.
Die Frau spricht mit dem Mann.
For example here or here
Herkunftssprecher seems to be what academia is starting to use as the German equivalent of heritage speaker. It is not a widely known word yet.
To call it a translation seems a far stretch though, Herkunft (meaning origin, provenance) is a strange word to use here, it's not a translation of heritage, which would be Erbe or Abstammung. I don't see how a an ...
"Herkunftssprecher" would work considering the definition, but I have never heard it used. If you grew up with german you could simply consider it your mothertongue which would be "Muttersprache", which would make you a "Muttersprachler"
Just because you don't know a language well doesn't make it any less your mothertongue