You can disable or enable spell checking in several ways:
•Click the
button and run the Settings command from the main menu. In the Settings pane, in the Spelling and grammar block, select the Check grammar checkbox.
•When working in macOS, select Tools > Spelling and grammar > Check grammar command from the command menu.
Enabling or disabling grammar check applies only to the current document and does not affect other open documents.
Grammar check basics
•The grammar check language is selected automatically by the first letter in the cell.
•The grammar check is run when you press Space or Enter, provided that the sentence is complete.
•A sentence with a grammatical error is underlined with a blue wavy line both in the cell and on the Formula bar.
•Formulas and their values are not checked.