Windows 10: Change default spellings in Mail WITHOUT changing OS language.

I want to change the default spellings checker in the Mail application to Dutch.I want to do this without having to change the OS language.I have read the articles on this site about a switch of proofing language but they don't provide an answer to my usecase.Having my operation system in english provides me with 2 major benefits.1. I can find the features I am looking for because I am used to it after 20 years.2. I can find helpfull articles when I run into problems because the dutch articles are non existend or worse then the english version.That said I find it irritating having to select t

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Change default language

Have a clients PC, Windows 10 Home, that the default language was changed from French (Canadian) to English by a tech for troubleshooting here . (Florida)
They're going back home (Canada) and wants the default language restored to the French.
I'm not the original tech and plead ignorance since I've never done this.
So I can here.
Anyone have a step by step?
Pete

 

Spelling or Proofing Language on Mail App for Windows 10

Old title: Spelling Language on Mail App

My primary language is english but I send mails mostly in spanish. How can I change de autocorrect option to spanish? I mean make it the default spelling check language. I have to type, highlight and change to spanish to make it work. Thanks

 

Default language for spelling check

On Windows 7 Professional, how do I change the default language that an existing Word document is spell checked in? Right now, a document sent to me was in US English; I've tried to change this to UK English, but the document now seems to change spell checker
language half way through it.

Thanks