Now that this has been dug up....
Since this doesn't concern the rules in Germany but does concern the rules and customs of another country (in this case, Australia), using the rules and regulations of Germany to dictate a translation makes no sense. Just because this is being translated into German doesn't mean it takes place in Germany.
A Marriage Celebrant is not a "Standesbeamte" -- they are not civil servants, and they are not some form of "-Redner" who simply guides the ceremony and delivers some sort of speech.
They are people licensed by the government to perform marriages.
Can't help with a translation, but those suggestions that indicate that it must be a "Standesbeamte" or is a "*redner" are off base.
RE #7 after 10 years:
(Hat noch jemand als Vorschlag gemacht, passt wohl für amerikanischen Kulturraum am besten. Ist aber in D eher unüblich sowas.)
a) Given that the OP indicates "Aust.", whatever takes place in the US is quite irrelevant here.
b) I've never been to a wedding the US that has had anything one could describe as a "Hochzeitsredner." Yes, pastors/priests/rabbis/familymembers or friends/ etc. may give a short sermon/homily/speech at a wedding, but there's nothing like some sort of official position to describe that.