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tester:
While master's degrees are a thing, I don't think anybody has ever used the honorific Master in English to indicate that somebody has one, except in the rare cases of persons with the surname Bates. In some trades, it is used to address or designate an instructor of apprentices.
Jonny69:
I don't think we have anything for that as a prefix. People who want to indicate that they have a Masters degree tend to put MEng, MSc or MA after their name. Calling yourself Master Xyz is the old fashioned way of saying you're a male under 18, you become Mister Xyz when you hit 18. I think that's correct.
You may both have misunderstood, and I probably didn't put that clearly enough. It's not a form of address in German, only an academic degree, and 'master' is its equivalent as an academic degree title.
I don't think we have anything for that as a prefix. People who want to indicate that they have a Masters degree tend to put MEng, MSc or MA after their name. Calling yourself Master Xyz is the old fashioned way of saying you're a male under 18, you become Mister Xyz when you hit 18. I think that's correct.