About [[MediaWiki:Poll-create-threshold-reason/en]]

You're most likely right. This message is related to $wgCreatePollThresholds (the "prevent users from creating new polls if they have less than X Ys" feature, where X is a number and Y is something like edits, votes, etc.).

The code is in /extensions/PollNY/SpecialCreatePoll.php, function execute (lines 56-77). I agree that proper i18n support for this would be very nice, but the feature itself isn't very widely used (if at all, but it's an useful feature to keep around nevertheless), so this isn't exactly a high-priority issue for me, but I'll happily review any and all community-contributed patches to address this issue. :)