Download mod from NexusMods https://www.nexusmods.com/baldursgate3/mods/775
Copy the “Public” folder and paste it inside of your Baldur's Gate 3\Data
Put your custom font files in Baldurs Gate 3\Data\Public\Game\GUI\Assets\Fonts\Replacers
Open the XAML file:
Baldurs Gate 3\Data\Public\Game\GUI\Theme\Keyboard.Fonts.xaml
And modify this line
<FontFamily x:Key="DefaultFont">/Assets/Fonts/Replacers/#ZhunYuan</FontFamily>
Make sure the font name is the same as the actual name of the file. The config does not recognize Chinese font names it seems.
I am using ZhunYuan and it looks like this in game:
LXGW Wenkai also looks realy good in game. Any font is better than SongTi which is the default Chinese font.