Korean works like this: all individual letters make up what are called syllable blocks that consists of anywhere from 2–4 letters. ㅅ and ㅏcan be combined to form 사, (“sa”). ㄹ + ㅏ + ㅁ can be combined to make 람 (“ram”). My colleagues have reported that individual Korean letters can be written in GZDoom without problems, but they cannot be combined to make syllable blocks. The letters end up scattered and separated like this:

Here is a short video demonstration of the issue. Whenever the user attempts to write combined letters, the chat simply doesn’t respond.
2019-03-20_23-30-03
I think this has to do with some kind of input issue. I was able to copy a Korean character into GZDoom just fine, but attempting to write it does not yield any successful results.