We are advised to not include Spanish language dialogue in an English language script. Rather, every character should, at first, speak English and then their words can be translated before production.
If only language and character could be so easily cleft.
If a character speaks English, she is thinking in English. If she speaks in Spanish she is often thinking through concepts that are distinct to Hispanic and/or Latin American cultures.
You may as well write a character as a man and then change him into a woman at the end. Her words, her self.
If it’s just a word here and there, and the meaning is obvious in context, don’t bother translating it. An example is when a ubiquitous foreign bad guy shouts at his men to do something. Since it doesn’t really matter what he’s saying, just use the foreign word if you know it. Sometimes, this type of dialogue doesn’t even make it on to the dialogue line, and gets summarized in the action…