I'm an American author whose book is set in a foreign country. I've received an offer from a publisher in that country. They want to translate the book, and publish it there. This is great news, but the market is very small. I also want to publish in the US, not just because it is a bigger market but also because it is my home. Should I hold off on accepting the foreign offer until (if!) I can work something out with a US publisher? If I do go ahead and publish abroad, then can I revise the MS for a US publisher or is it set in stone and unrevisable once published?
If it's a very small market, your US publisher may not mind your having sold the rights already. And more and more, agents seem to be going after foreign sales for their clients, so publishers are a bit more accustomed to not having a lot of foreign rights for novels. So that's unlikely to be an issue.
As for revision, every translation fiddles with the exact phrasing of the text--if it doesn't then the translation won't sound natural to native speakers. So some differences between the English and other language editions are expected.
So if there were some way for you to be sure you weren't going to do very much revision (for instance if you've decided already that you're going to be inflexible and hard to work with--which I assume is not the case), then there would be no problem. But imagine your US editor has a bunch of suggestions that get you really excited and that (for instance) change the ending completely.
There probably still wouldn't be a problem with copyright between the two editions, but how would you feel about that scenario? Would you want two very different versions of your story out there--when one of them might end up feeling to you like a beta version and not the story you most want to share with readers?