Hi Daniel.
There should be no need to propagate contributed translations any more. They should be automatically committed in a way that they apply since the oldest possible version. I just checked the timeline history of some of the strings that came as a part of recent contributions to pt_br #37466, #38096 and it seemed to work ok.
There is still an open issue affecting translations import MDLSITE-6394 though.
Maybe you could provide more detailed step-by-step description of how to reproduce your problem?