Only Brazil do not have Spanish as an official language. The official language in Brazil is Portuguese.
Here is a list of South American countries that do not have Spanish as an official language. Some of these countries speak spanish as a common language though, even though it's not official:ArgentinaBrazilChileFalkland IslandsFrench GuianaGuyanaNicaraguaSurinameUruguay
Spanish is the language spoken in more Latin American countries than any other, as it is the official language of most countries in the region.
Brazil, Guyana, Surinam are three countries where Spanish is not the official language. French Guyana is a territory in South America where Spanish is not the common language.
The official language of most Latin American countries is Spanish. However, in countries such as Brazil, the official language is Portuguese. Additionally, some countries have recognized indigenous languages as official, such as Quechua in Peru and Guarani in Paraguay.
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Swahili
There is no language that is spoken in all South American countries except one. You're thinking of Spanish, but Spanish is not spoken in:BrazilGuyanaFrench GuianaSurinameThe Falkland Islands
Castellano is the another way to say the spanish language in spanish.
Spanish is spoken in many South American countries, but it is only "official" in these 7 countries: Colombia Peru Venezuela Ecuador Bolivia El Salvador Paraguay
The Central American countries that speak Spanish are Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, and Panama.
Spanish is spoken in the greatest number of Latin American countries, with 19 countries in the region using it as their official language.
Spanish - because most of the South American countries speak that language, and Brazil because it is spoken in the largest country on the continent.