From @Slaporte: Here is my suggested copyright line for the data tables page:
Data available under Creative Commons Zero v1.0 Universal, or (at your option) any later version.
We can also shorten the CC0 text for the sake of readability, since specifying "v1.0 Universal" is redundant with the hyperlink, and especially now that there is only one version of CC0. I'd recommend using a short form like this for the sake of usability/readability:
Data available under Creative Commons Zero.
The shortened form is slightly less precise, but it is consistent with the human-readable approach we use in the footer and elsewhere.
On the edit page, you can use the same template as the MediaWiki help pages as Yuri suggested. You can also can also change the copyright message (above the save button) like this:
When users enter a license other than a valid version of CC0 (eg, "CC0-1.0+"), I would recommend revising the message that appears to explain the restriction in more detail and provide a link back to the help page with more info:
//We currently only accept public domain data under Creative Commons Zero. For the "license" parameter, you provided [some wrong license name]. The license must be: "CC0-1.0+"
For more information on licensing in tabular data, please see the documentation.//