Same symptoms: https://bugs.mojang.com/browse/MCL-22070
Korean is missing in minecraft launcher(2.3.324)'s language setting.
As described in the picture(=k.png), there was Korean in that location, but it disappeared after the update.
As a result, it became impossible to set it in Korean, and the user previously set in Korean was changed to English.
Although it is set to KO-KR like ks.png, it is not displayed in Korean.
Thank you for your report!
We're tracking this issue in MCL-22070, so this ticket is being resolved and linked as a duplicate.
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