A family of Microsoft word processing software products for creating web, email, and print documents.
Language is a character-level attribute of the text. The Default only determines the Language used when starting a new document.
Apparently there is text in the document which carries the Portuguese attribute. If all content is to be in a specific Language use Command+A to select all then go to Tools> Language to apply the correct one. Otherwise, it's necessary to select the specific passages to be changed or use a Style which includes the appropriate Language.
Also, make sure the box for Detect language automatically is not checked and go to Word> Preferences to confirm that Match font with keyboard is not checked unless you're familiar with it.