Currently, there are 9 questions under [polyglot-programming]. IMHO, the use of this tag is not justified for most of theses questions. For instance, one question relates to both C# and F#, and has these two tags. No need for an additional tag.
I believe there are many other examples of such tags that add entropy to the site instead of decreasing it.
AFAIK, if these questions are edited to remove this tag, and no other question is tagged under it, it will be automatically removed from the system after 24 hours.
Why not reward the user who untags the last question under an obscure tag, thus causing it to be removed?
Of course there must be some criteria for a tag to be considered obscure, let's say it must have been created at least
x months ago, and must not have more than
y questions in total.
I thought of some names for such a badge, "Garbage Collector" may be too obvious, "Vulture" may be somewhat disgusting. :-)
That's it, just a discussion to kill some time :-)