How do I remove red underlines in my emails?

I have an iMac from 2010. I recently wrote an email in French and now many words are underlined in red in my emails. I tried to change the language setting on my Chrome browser using advance settings, but was told that if it's on an iMac, I have to go to Apple. I am not a high powered user so is there a simple fix for this? My primary language is English.