According to the lists, Display Language may "depend on your mobile operator or phone manufacturer."
Keyboard "input languages are available on all phones, regardless of which display languages your mobile operator or phone manufacturer chose to include."
I assume Korean selection yields Hangul... Someone will correct me if I am in error.
Have you tried ensuring your Region matches the Language you require?
It might help to know the exact model and if it is carrier branded or not. What RM # etc...
Last resort, make a backup and do a factory reset. Then select the language you desire during setup. Sign into your Microsoft Account and restore your backup.
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