Recognizing that the national language of Brazil is Portuguese and not Spanish shows an awareness of what sort of difference?

Ethnic differences.

Explanation:

Ethnicity describes the culture followed by the people native to a particular geographical area or region.

Ethnicity for a region includes following cultural factors like

Language

Heritage

Religion

Customs etc.

The ethnic values makes a region different from other regions.

An individual is said to be a member of an ethnic group when he conforms to some or all of the practices of the ethnicity of the region.