Although I am software developer I have always had interest in foreign relationships. As a Brazilian I always saw Brazil talk first at the United Nations (UN) General Assembly (GA) but never realized how curious it was.

Brazil is not the first member of the United Nations, it is one of the 50 founding countries. It is not the greatest economic nor military power and is not even at the UN security council. Regardless of our economic or political situation, even during our dictatorship years, we have been the first country to speak at the UN GA, even before the host country!

The reason, according to a quick Google research, is that in the early meetings of the General Assembly no country wanted to speak first. Probably as speaking first was seen as a compromise and a burden.

Brazil, as a neutral country throughout history, saw no problem and since the 50's volunteered to open the UN GA by being the first to speak.

After a few years of being the first to volunteer to talk, it became an unwritten tradition that follows to this day, decades later.