Portuguese to English Social Sciences Social Science, Sociology, Ethics, etc. Demography

The text is about the status of education in the state of Bahia, Brazil. Does this mean that only 4% speak their native language - compared with 37% for Brazil's entire indigenous population? Or could it possibly mean that only 4% of them speak [the country's] language--i.e., Portuguese--compared with 37% of the country's indigenous population? [There's no further context.]

Os indígenas são mais de 17 mil indivíduos, de 22 etnias. Dentre os indígenas baianos de mais de 10 anos, 17% são analfabetos, quase o dobro da média do Brasil (9%), e apenas 4% falam **sua língua**--a média Brasil é de 37%.