Can't switch spell checking languages

Could somebody please tell me how to manually switch languages for spell checking? I write in US English and the checking is done in UK English…
Thank you.

Are you on iOS or macOS? I would expect that Spell checking follows the language of your keyboard, so double check your keyboard language.

In any case, it is not something that we set explicitly. It is something set at the operating system level, either in the Settings app, or System Preferences (Mac).

Kind regards,