If you are having problems switching to Chinese in Little Nightmares, please try the following.
Go to the game's directory, default:
C:\GOG Games\Little Nightmares
If you are using the GOG GALAXY Client, click the game, click MORE > Manage installation > Show folder.
Open the goggame-1433377508.info file in a text editor and replace the following line:
"language": "Chinese (Simplified)",
You can also try replacing the file with this one.