In T123129#1571915, @Alwin wrote:

Hi,
Not all problems on this page can be solved by us, oftentimes there is a problem in the player's PC and the only thing we can do is give him advice.

For your reassurance. Your issue was "Acknowledged", reported to programmers and will be managed.
It will take a some time so I´ll ask you about patience. We´ll inform you as soon as possible.

2020 and not fixed yet

May 2020, Still not fixed.

soon with sensors update.. AAs with radar will be less likely to be detected and counter them when they pass the area.

Alwin, Korean input in arma 3 is indeed supported. Some of my friends really don't have any issue using korean in game in full screen mode. But some others exprerience the BUG. This can be fixed and if this is not solvable in feedback site, what's this site for? As a loyal player of arma 3(I Bought all the DLCs in normal price) If this is not solved, I must be very disappointed.

Hello?

I changed language in Launcher.
And the problem is 100% reproducible for me and some other friends. But also others dont experience it.
And I use laptop so I don't have a cable beteween monitor and computer.
Reinstalling didn't help.
When I try to use korean I see the small window showing what I'm typing on the top left side of the screen. and screen goes to window mode.
What I want is not forced window mode. So I disabled it.