As I said:
The only citations about languages are
"Preferred Languages> Websites Will Show Content in Your Preferred Languages, When Possible"
AND
"Spell Check> Use Spell Check For"
Both have my standard language selected and yet Opera continues in English.
It is important to make it clear that my Kubuntu's default language is Portuguese and not English and the other browsers on my computer (Chrome, Firefox, Brave and Edge) are in Portuguese. Only in Opera this bug happens.