You are godlike for acquiring this information and sharing the firmware!
One question out of curiosity: I understand from the above text that the checks are in the firmware and in the application server software (sonia).
Does that mean that once your modified firmware is flashed (and so sonia is patched), and afterwards an official US firmware is flashed, then your camera is now officially an US device (you can now always install any official US firmware provided they don't check in the future on a modified sonia) ?
Well, you'd certainly be able to flash a US firmware image if you have one that supports your device. I have not found an image for the newer Eos (gen 3) cameras, only previous Themis (gen 2) cameras.
And from that US image you'd also be able to flash another US image. Probably not the chinese one however, unless you change the chinese check.img.raw to English:
Code:
"DefaultLanguage" : "SimpChinese",
"DefaultVideoStandard" : "PAL",
"SupportLanguages" : "SimpChinese",
I would not recommend using the US images as they seem to lack some features (H265 because of licensing issues...)
You are free to experiment however, the check.img will prevent you from flashing an incompatible firmware image.