Holy shit this is some primo conspiracy shit. You're reading meanings from character encoding quirks?
Is that really necessary given everything that's just in plain text? Is there any evidence that this is actually encrypted Chinese text at all? Do you have any understanding of Chinese or are you just trying to find meaning character by character?
Have you checked your technique against random chunks of other text data to ensure it's not just a coincidence?
And most of all, why the fuck are you doing this work and sharing it through google if you think there's even the most remote chance you're actually onto anything?
I honestly don't have anywhere near the kind of knowledge in encrytion and character encoding to even begin to say if you're on to anything or not. I doubt you do either, or else you wouldn't be asking here.
Considering there were csam images as unencrypted images in the files, I find it hard to believe they even cared to try and hide anything. Especially not under a reversible encrytion with some character encoding shaningans. More likely they would have used one of the many standard methods that rely on secure key exchange through a separate channel and asymmetry.