I have same kind of plans as starter. We are both foreigners and wish to get married in Namibia. I have phoned magistrates court in Windhoek (yesterday 31.8.22). They told me that the first thing is go to Department of Home Affairs and find the "immigration" and get some kind of document from them. Immigration will ask police clearance and impediment of marriage certificate and these documents must be with apostilles. These documents must come from your home country officials. Valid passport is also required.
Next thing is to book time for wedding in magistrates court. To be able to book the wedding time one has to have the document from "immigration", inpediment of marriage certificate, police clearance document and valid passport. The wedding itself cannot happen until one month from the booking.
The thing is bit tricky as we are not able to spend more than two weeks in Namibia. Maybe there is a way and I'm still trying to find out more. Information seems to be little bit conflicting. If anyone has any advises I'll be glad to hear.