My Windows is in English and I use Brazilian Portuguese (PT-BR) as the secondary language for the system. I'm using Edge browser with the lastest updates, this problem has been happening for around 2 years already.
Outlook Web doesn't perform spellchecking for PT-BR, only for EN.
Here is the problem that I'm having. As you can see I'm using an InPrivate anonymous window, so cache issues are out of question.
My spellchecking options:
Switching the keyboard language at runtime doesn't do any effect.
I don't have any issues on other sites, like while writing this post: Maçã. Correio. Preço.
Only in Outlook Web.