You may be editing an MS Word document that uses two or more languages. The automatic spell checker marks in red all errors in all languages. If one of your languages is not covered properly by Word’s checker, so that all of it is marked in red, you may prefer to suppress the checker for that particular language only.

If Word followed always common sense, you would be able to find in the Proofing section an option to disable spell checking for a language. However, there is no such option in Word.

A way to disable proofing for a particular language is to use a unique style for that language, then in the properties of that style (Format > Language) select the language you want proof-free and check the option “Do not check spelling or grammar.”

Another way, useful when you already have written all the text for that language, is to select your text, then go to Review > Language > Language > Set Proofing Language, then select the language you want to free from the spell checker and check the option “Do not check spelling or grammar.”

Enjoy!