In the reopen queue, I attempted to vote to keep it closed, and I selected the last option -- "This question doesn't meet a Programming Language Design and Implementation Stack Exchange guideline." However, when I clicked the "Keep closed" button, I was given the error message "Please select a site specific close reason". I don't see any. Is it not possible to select this option?
This is an (unfortunate) side-effect of this site not having any site-specific close reasons yet. For clarity, a site-specific close reason is a close reason that's listed under "Close -> A community-specific reason" (or as you observed, in review, "Leave Closed -> Doesn't meet a (site) guideline"). So... This really is a bug that should be fixed with a more intelligent error message, but can be fixed by creating an applicable site-specific close reason.
Now... A lot of new sites or still-in-Beta sites don't typically have a need for site-specific close reasons. The existing close reasons (Duplicate, Opinion-based, Needs more focus, Needs details or clarity) are broad enough to encapsulate most of what might be wrong with a question. Where those fail, you can use a "Custom" close reason when voting to close ("Close -> Other"), but sometimes you want to pre-package a close reason and pack it full of helpful information for the asker, the closer, and any future visitors. That's where a site-specific close reason comes in, and that's where the community needs to come together and decide how that close reason should look and in what situations it should be used.
We appear to already have a question about what community-specific close reasons we should have here, and I've gone ahead and created an answer there based upon info that was previously in this answer that explains a little bit more about what's expected of a new site-specific close reason, which may be of interest.
