You can remove words from the custom dictionary in opera.
But how do you remove words from the standard dictionary?
I have the British English dictionary, but for some reason, it also includes American English spelling.
Symptoms:
Spell check accepts American English words & spelling, instead of British English.
For example:
"Spelled" is accepted, "spelt" is not.
"Summarize" is accepted, "summarise" is not.
Attempted fixes:
Adding each word to custom dictionary. However, the incorrect spelling is still accepted, and I don't want that.
Double checked that the American English dictionary was removed. (It was.)
Double checked that I have British English set as the display language. (It is.)