umm just to correct you but brazil is not the only country in south america which doesn't speak spanish. There is also the French speaking French Guiana, the dutch speaking Suriname, and the English Speaking Guyana. Non of these countries speak spanish. The reason behind the difference though is because brazil was a former colony of Portugal and these other countries were colonies of the respective European countries to which each language belongs to (e.g. Suriname was a former Colony of the Dutch). All the other countries had influence from the Spanish who voyaged the New World such as Francisco De Oreallana. Pretty much if the country was colonized by a European Nation they adopted the language of that nation. However, they normally took the language of the nation which colonized them last because some of them like Guyana were colonized by all the nations, the birtish colonized them last.