São Paulo Mayor Ricardo Nunes Thursday sent a by to the local City Council whereby Guarani would be declared the second official language of South America's largest city.
The project envisions the use and learning of Guaraní in schools and media, especially within local indigenous communes.
It also foresees the production of public documents and institutional advertising campaigns in both languages, Portuguese and Guaraní.
Although the initiative was formally introduced in July, it became widely known Thursday after it was published by the Brazilian magazine Veja.
More than 250 languages are believed to be spoken throughout Brazil, of which 180 belong to indigenous peoples.
The project also provides for a translator to be available when necessary, to avoid discriminatory actions and for a demographic census of the indigenous population every five years.
According to the latest census of the Brazilian Institute of Geography and Statistics (IBGE), the Guaraní population in the state of São Paulo was 4,138 people in 2010, about 6% of the total Guaraní population in all of Brazil.
In the city of São Paulo, one of the main ethnic villages is Tekoa Pyau, in Jaraguá, northwest, with approximately 600 indigenous people.
Guarani is an indigenous language present in South America, especially in Argentina, Brazil, Bolivia and especially Paraguay, where it already is the country's second official language.