Is there really no Spanish option? How can you poll NV and AZ without a Spanish interviewer or questionnaire
Don't be silly: If you are smart enough to register for the YouGov online panel in ENGLISH, you are also smart enough to fill out a simple question that asks "Are you voting Clinton or Trump ?"
No Spanish needed.
But Hispanics who would respond to a poll in English are different from those who would respond to a poll in Spanish. The two groups wouldn't necessarily vote for Clinton and Trump by the same margins. By not having a Spanish language option, the poll misses voters who would only respond if there was such an option.