UPDATE:
I've updated the close blurbs for 1 and 4 below to match the text I've proposed. I haven't updated 2 because there was some ongoing discussion about site scope that seems to need to wrap up before we change the wording here.
I didn't update 3 because it was already customized so I wasn't sure whether I should leave the current version or update it to my proposal below. The current text is:
This question is off-topic, as it is specific to an unsupported release of Ubuntu. It is not currently accepting answers.
I've been working on these edits across the network off and on for different sites - as such, I'd like to throw some alternatives at y'all based on my experience. Feel free suggest changes or decide the other version is better if you want.
Before I get into that, I will confirm that I've had a discussion internally and, while I don't know when it will happen, the consensus is that we will eventually be showing the full close reason to everyone (again).
Also, I'll take a minute to plug my guide to writing close reasons on Meta Stack Exchange. While I'm OK with making this interim change because I agree that the short form is often not useful or downright wrong - i.e. not all community-specific close reasons are "off topic" at all - I'd love it if y'all could work on improving the full five fields that can be updated.
If you have questions about this, let me know.
1. Not about Ubuntu
Full text:
This is not about an official Ubuntu flavor. Questions about other Linux distributions can be asked on Unix & Linux, those about Windows on Super User, those about Apple products on Ask Different and generic programming questions on Stack Overflow.
Your version:
This question is off topic; it's not about an official Ubuntu flavor.
My recommendation:
This question was closed because it is not about an official Ubuntu flavor. It is not currently accepting answers.
2. Bug reports
Full text:
Bug reports and problems specific to development version of Ubuntu should be reported on Launchpad so that developers can see, track and fix these issues.
Your version:
This question is off topic; the issue should be reported as a bug.
My recommendation:
This question was closed because it should be reported on Launchpad as a bug. It is not currently accepting answers.
3. Unsupported Ubuntu versions
Full text:
End of Standard Support or End of Life Release
This question is specific to a release of Ubuntu which has reached its end of standard support or end of life date, and is not related to asking for help to upgrade to a supported release. Such questions are considered unsupported and off-topic on Ask Ubuntu.
Your version:
This question is off topic; it's specific to an old unsupported release.
My recommendation:
This question was closed because it's about using an unsupported release of Ubuntu. It is not currently accepting answers.
In this one, I thought that "using" might bring the focus to the use of the release as opposed to the upgrading away from it - which seems to be allowed. That said, I'm not sure whether "using" captures the full scope of this close reason. I also said "of Ubuntu" since that's what the link goes to - it doesn't seem to be used for flavors other than real Ubuntu.
4. Can't be reproduced.
Full text:
This describes a problem that can't be reproduced, that seemingly went away on its own or was only relevant to a very specific period of time. It's off-topic as it's unlikely to help future readers.
Your version:
This question is off topic; it's about a problem that can't be reproduced.
My recommendation:
This question was closed because the problem as described can't be reproduced. It is not currently accepting answers.
General notes:
I've removed "off-topic" from these because it's something that ends up being a thing people can argue about or get hung up on. I find just saying that it's closed and why can be neater.
The "It is not currently accepting answers." is going to be the sort of default we add to all close reasons.
I've omitted the links in these short versions of close reasons because I'm a bit concerned about cases where they're the same link that's going to appear in both the short version and the long version - it means that the asker and high-rep users will see the same link twice, but with different text, which readers tend to assume will be a different link, not two separate cases of the same link. I understand wanting to have the link in the short version but it might make sense to think about whether it should also be in the long version.
This is, again, an argument to refresh these entirely with wording that is more targeted at the people who will be seeing these notices.
Also, if you like the headers I used, I can go ahead and make them the "name" of the close reason, which will make that the quick-reference term used in the close dialogue.