How to change preferred language in Word

I recently started learning Spanish for a class, and I thought it would be nice for when I write in Spanish on documents to have it recognized as another language, so I added Spanish as a preferred language. This actually did the exact opposite of what I wanted, and now my Word documents don't recognize English as a language, and it red underlines every English word that I write. Is there a way to fix this? I almost entirely speak English, but it's just this one class that requires Spanish. My display language is still set to English