I have a reasonable idea for a feature request.
When a user is creating a tag the system will recognize that and point out that the following tag is new, requiring the user to acknowledge the creation of the tag.
Possibly the message can show the names of similar tags (e.g. creating the tag complex will show the name complex-numbers and complex-analysis and so on), and point out that it might fit under these tags instead of creating a new tag. The shown tags can be selected based on the tag name alone, or by searching the tag wiki excerpt for words appearing in the new tag (e.g. if I were to create a tag cardinal-arithmetic then a suggestion to use cardinals instead should show up, as the tag excerpt contains such term).
My view is that such message should show for each and every new tag created by the question, so if someone decides to create five new tags, they should authorize five different tags.
This may help decrease the creation of essentially-duplicate tags, or new and essentially-over specific tags.