One fact of reality is that Standard Ebooks' tooling is English-based. Everything from the pages/xhtml it generates to its typography tools to its style guide expects English. For example, Spanish uses — and «» instead of English's “” and ‘’ for dialogue so you can imagine how SE's punctuation tooling heuristics are going to differ here.
You'd also have to come up with a new set of standards for another language. What sort of correction is a fair modernization and which would be unfair editorialization? SE itself already makes controversial decisions here for English like "to-day" -> "today".
It would be a large undertaking to parameterize some sort of LANG=EN setting and imo not worth it. I think the only route for that sort of thing to happen is if 2+ "forks" get to Standard Ebooks' quality and then decide to work together years down the road.
Also, legal clarity is sometimes an issue in other countries where an English translation written in the USA of that same work is clearly in the public domain. There are works where the original non-English content, despite being long translated into English, are still owned by the estate, but the English translation is liberated.
Something I realized was just how many books exist only as scans. Transcription isn't very fun, but this makes it rewarding. For example, I have some early Spanish sci-fi books I've transcribed into epubs that you cannot find outside of dirty scans.