Korean' entered in Jira custom fields is broken

Jira 7.12.3

‘mysql’ Specific ‘fields’ have ‘Korean’

I entered this ‘Korean’ into ‘Jira custom fields’ using ‘Jira REST API’.
As a result, ‘Korean’ is broken. (Below)

Let me know why and how to fix it.
Waiting for help.

I have problems in my jira server too with chinese characters
𦴥< 𦴦 <𦴧<𦴨<𦴩<𦴪<𦴫<𦴬<𦴭<𦴮<𦴯<𦴰<𦴱<𦴲<𦴳<𦴴<𦴵<𦴷<𦴸<𦴹<𦴺<𦴻<𦴼
all those are not working I think the code for those begin by 0xFF…
not sure it is the same problem you get

You can check you have the good coding of character Unicode / UTF / Iso