Works fine for me with and without setting MUI_UNCONFIRMPAGE_TEXT_TOP.
PHP Code:
!include MUI2.nsh
!insertmacro MUI_PAGE_INSTFILES
!insertmacro MUI_PAGE_FINISH
!define MUI_UNCONFIRMPAGE_TEXT_TOP "시스템에서 $(^NameDA)(을)를 제거 할 것입니다. Blah blah more text $_CLICK"
!insertmacro MUI_UNPAGE_CONFIRM
!insertmacro MUI_UNPAGE_INSTFILES
!insertmacro MUI_LANGUAGE Korean
Name "long name here to wrap lines"