The original plan
Most of the internationalization work took place before I was hired, so I am only privy to the details that were shared publicly. Part of the detail that I am familiar with is that we initially only planned to create Stack Overflow sites, and only for languages which weren't already well-served by the existing English community. As in, having many developers that did not speak English and could not effectively participate there.
There was never a plan to create other sites fully with non-English interfaces. There was only ever a "let's see what happens with this experiment" and a hope that it would expand into something more. It never did...
So there is no infrastructure prepared for non-SO non-English sites because we never planned to make those sites in the first place.
So what happened?
There were some roadblocks that prevented the overall vision from succeeding fully. In particular, we had initially planned to launch a Stack Overflow in Arabic site. It never came to fruition because supporting right-to-left translation throughout the entire interface was much harder than anticipated and we never implemented it, opting to close down the proposal instead.
The International Stack Overflow project was also largely spearheaded by people who no longer work here or have transitioned to other teams. Only two of the community managers who were heavily involved in the international sites still work on the Community Team to this day. Launching sites in new languages is exponentially more difficult than launching a standard English site, even without the technical considerations I mentioned in the other post. That is why we've previously mentioned that we require a Community Manager fluent in that language to be hired before we were willing to launch a site in that language. We just can't pull it off without that connection to the language.
But past that, without the team that once worked so much on internationalization, the project just kind of died off. Priorities shifted, and the idea of launching more non-English sites fell off all the backlogs over time. I'm sure someone will want to pick back up and run with it at some point, but it's not currently on anyone's radar that I know of.
Don't get me wrong: we consider the international sites we did manage to launch resounding successes. Their success just never catalyzed further site creation like many expected.
I wish I could provide you with more information on the intentions there, but a lot of this information has been lost due to the transitioning of information between different systems over time and the original people behind it no longer working here. If you can't find it in public posts here, you're probably not going to find it.