Fair enough. But SE's creator is simply going to recommend that you fork the project. Not that I speak for them, I've just been following the project long enough to see the interaction many times.
It's also the only avenue that makes sense. As I said in a sibling comment, I've been working on a Spanish-language version of SE and I have some good ideas of how the tool chain could be parameterized for multi-language support, but it also feels like a pointless cherry on top (and a complication of an already non-trivial workflow) to bring everything under one umbrella. And it would require a loss of control for SE's creator.
I recommend epub'ing a few book scans yourself in your preferred language and starting a project around that. You'll find other people who have at least started a fork themselves that you might be able to round up under one org. I personally have aimed for 10 ~finished books and a domain name that hosts my own style guide + tutorial to prove that I'm serious about it (to myself) before I publish my efforts. And you need as much to appeal to any would-be contributors.
I think the only plausible place to be in 5 years is for a couple major sister projects to reach maturation and then form a sort of ring of "Check out lettres-libérées.org for a similar project for French works."