Outlook Web spellcheck not working for secondary language

Hello

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:

Language settings:

Windows settings:

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.