I don't know in the console how to see if images or files are loaded when it comes to canvas.
But all I know is that every language buttons (ES and FR) lead me to the story in english.
What I mean is:
"assets/gui/LANG/splash.png"
This means you should different splash screen, one per language. Is this being loaded correctly?
I have :
"assets/gui/EN/splash.png" "assets/gui/ES/splash.png" "assets/gui/FR/splash.png"
And it every time loads :
"assets/gui/EN/splash.png"
Then the problem is in the language chooser, it's choosing always english. The key must be in the LanguageChooser.js file, I'll check again if there's a problem with the example.