People won’t know where the message comes from, they’ll just hear your voice as though you were standing next to them. Everyone hears it at the same time. The message is not translated into anyone’s native language, everyone hears it exactly as you say it. The maximum length is 6 of your breaths.
I don’t see why you’re acting so supised, the plans have been on display at your local galactic planning office for 300 years.