Sorry, I know the solution was in the forum way back in the early days, but I can't find it anymore:

When I type a name for my char, every character comes out double.

This post on steam explains both the problem and the solution, but I don't know how to apply the solution:

https://steamcommunity.com/app/640820/discussions/5/1734340257880761823/

Can someone help me out here?

I don't have the problem myself, but to apply the described fix, just edit start.sh. Add the environment setting to the line that invokes the executable. In other words, change
./"Kingmaker.exe"
to
XMODIFIERS= ./Kingmaker.exe
You don't have to remove the quotes if you don't want to, but they're all unnecessary.

Alternatively, just add a line to the top of the script:
export XMODIFIERS=

That would work, thank you.
Since I'm using Lutris, I found out that I can set this environment variable under "System options". Just adding "XMODIFIERS" as key, and leaving value empty does it.

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