There are no subtitles accompanying the Spanish lines of dialogue, because, well, there are no subtitles in life.
In the film, Miles Morales (Shameik Moore) is the son of a Puerto Rican mother and an African-American father.
This is representative of the home life of many biracial families.
Miles and his mother, Rio (Luna Lauren Velez), speak Spanish to each other throughout the film, notably during one of the earlier scenes in which Miles is getting ready for school.