i assume he's a canon character whose origins you don't have much info on—b/c that's not giving much to go off of. was he born in the US? is he fluent in spanish? were his parents wealthy? first generation? does he live in LA? Texas? Ohio? it varies. and honestly, i'm sure you could gloss over things like that if they're not supplied in-canon.
and if he's an OC, hell you could keep it simple and make him a total coconut

as far as language goes, just know that mixing spanish and english words in a sentence is generally not how bilingual people talk (and i hate how often writes do that shit for their brown characters) unless they're speaking with someone who's also fluent in both languages. regardless of his fluency, he's probably not gonna say some spanish phrase while talking to someone who speaks english/wouldn't understand it. if you're gonna add in spanish, do it in interjections or maybe if he's talking to himself or something.
personally, i prefer writing something like "he curses in spanish," or "he mutters something in spanish about how he hates butterflies" to actually translating. because connotations are hard . but if you need it, wordreference.com is your friend, and stay away from google translate.