Hi David!
I am glad you were able to create such a nice taxonomy structure, that should make your future work a lot easier.
So, by default, the taxonomy term follows an ‘all terms should match, exclude unchecked’ logic for the checkbox layout. In most cases this logic is expected. This means, that selecting ‘Chineese’ and not selecting ‘English’ will exclude those that have both languages assigned obviously (since ‘English’ is unchecked, meaning we don’t need those). I would rather not go into more details, it gets really complicated in no time 🙂
You can change this logic of course, I think in your case a more loose one will work better. Change this option to ‘at least one of the selected terms should match’ value.
This will make sure, that any of the checked values is sufficient for a match, and the unchecked checkboxes are not treated as exclusions.