Currently, Spanish is the main official language of Puerto Rico:
P. Rico Senate declares Spanish over English as first official language
The Puerto Rican Senate approved a bill Thursday declaring Spanish as the first official language of the country, relegating English to second position.
Thursday's bill proposes to establish Spanish as the first official language making its use compulsory in executive, legislative and judicial matters, and thus repeal Law 1-1993 which put both languages on an equal footing.
Also, Languages section on Wikipedia says:
The official languages of the executive branch of government of Puerto Rico are Spanish and English, with Spanish being the primary language.
Spanish is, and has been, the only official language of the entire Commonwealth judiciary system, despite a 1902 English-only language law.
If Puerto Rico votes to become USA's 51st state, what effect (if any) would it have on Spanish being the primary official language?