When i write text in Korean, I had two problems.
The first issue like below:

If I type Korean in the first input, the editor does not receive the contents.
But I typed Korean after the first, It worked.
The second issue like below:

When I write in Korean and change the next line, the last letter will be lost.
latest? 1.14.2?
https://prosemirror.net/ <- this version
If you aren't enough the above information or need additional information, please comment anytime.
Hi, I'm a Korean developer also using Prosemirror in my project.
My prosemirror-view patch below will work for you.
I also fixed another issue that you don't have reported.
That is an issue where the selection would change to next line
when deleting content during composition of the first letter of a sentence.
Hope this will help you.
Most helpful comment
Hi, I'm a Korean developer also using Prosemirror in my project.
My prosemirror-view patch below will work for you.
I also fixed another issue that you don't have reported.
That is an issue where the selection would change to next line
when deleting content during composition of the first letter of a sentence.
Hope this will help you.
https://github.com/ProseMirror/prosemirror-view/pull/69