Fix spell check on your Mac when it uses the wrong language

Why it happens

Your Mac checks spelling against one language at a time, or guesses the language as you type when Spelling is set to Automatic by Language. If it's set to a fixed language you don't use, almost every word gets a red underline. Writing in two languages can confuse the guess too, so autocorrect may change words into the other one.

How to fix it

1. Open the Apple menu, choose System Settings, and click Keyboard in the sidebar.

2. Under Text Input, click Edit next to Input Sources, then find the Spelling menu and pick Automatic by Language. If you only ever write in one language, pick that language instead.

   Keyboard›Text Input›Edit…›Spelling

3. For British, Australian or another kind of English, pick that exact one from the Spelling menu, not plain English.

4. Writing in several languages? Choose Set Up in the same menu and tick each language you use, so Automatic by Language only picks between those. Click Done when you've finished.

Still not fixed?

1. If one document still shows the wrong language, the app may have its own choice. In that app choose Edit > Spelling and Grammar > Show Spelling and Grammar, and pick the language in the panel.

   TextEdit›Edit›Spelling and Grammar›Show Spelling and Grammar

2. If autocorrect keeps swapping words into your other language, turn off Correct spelling automatically in the same Text Input settings.

   Keyboard›Text Input›Edit…›Correct spelling automatically

3. If a name or word you use a lot is always underlined, Control-click it and choose Learn Spelling. Your Mac stops flagging it.

4. If spelling keeps going back to the wrong language after you change it, restart your Mac and set it again. If it still won't stay, contact Apple Support.