Update is out.
@jair101: It turns out my copy had some fixes for special chars on tag management from some months back. They're included.
Notes of caution on this update:
Clubs: Club forums are just like regular ones, except for the part where they aren't like them in any way. You can edit them in the admin by going to Clubs > {edit club} > Forums > {edit forum}. The normal tag/prefix settings will now appear there. These settings cannot be changed from the frontend by the club owner. I have no intention of changing that.
Tag quick-edit: This should respect context settings now (forum-specific tag restrictions, etc.). BUT IPS bakes prefix handling into that same input, and gave me no way to change that. That means the prefix can be changed from the tag list with no regard for permissions or prefix restrictions. The only alternative is having tag quick-edit unset any prefix entirely, which seemed worse. There's nothing I can do about it.
Mage Tags: I revamped the manage tags section out of necessity. The old DB table it was using before gets worse with every release. The new one should work more reliably (no more page count bug!), but I have no idea how well it will scale for sites with thousands or millions of tags. If the answer is 'not well', my ability to improve that is probably limited.
What's New in Version 3.1.9
This release targets IPS 4.2. Backwards compatibility to 4.0 is likely, but not guaranteed.
Added tentative support for Clubs forums (settings can be edited via Club forums in admin).
Added tentative support for tag quick-editing on frontend. Note: Prefixes fall back to default functionality in that context; this is unavoidable.
Refactored Manage Tags section to fix SQL grouping errors and paging quirks.
Improved caching performance.
Fixed some instances of tag case insensitivity.
Fixed lingering tag edit/delete encoding issues.