The secret word list would need to be curated and digitally signed by several parties, including data security advocates to ensure that it doesn't simply contain the entire dictionary.
Also, having a secret, local wordlist is a challenge. Eg. What is stopping someone from testing every possible one-word message, using the reporting functionality as an oracle?
Then the secret word list might include stuff like "free speech" or "Uighur" and the world would go to hell.
* Who do I trust to look at the pictures in the government database?
* Who does the government trust to look at these pictures?
* Who would even be willing to look at these pictures?
These are probably disjoint sets, leading to a very empty intersection. Unfortunately, the logical impossibility of a government implementing a system that citizens should be happy with is not a barrier to it implementing some other system which it claims is good enough.