A user has reported that inputting Korean into certain types of text boxes in the editor using an IME results in delayed input. The user reports that this occurs with SMultiLineEditableTextBox in the SlateViewer or EditableTextBox(SEditableTextBox and SMultiLineEditableTextBox) in a Modal window.
The Windows IME for Korean was used to test this originally.
This occurs in 4.18, 4.19, and 4.20
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-66315 in the post.