I agree, speech and spoken-language seem to have a good degree of overlap. One option is to merge the two tags.
I am not too keen creating tag wikis for speech or speech-rate, quite the contrary, I'd prefer these tags deleted. This is my rationale: rather than think of these tags as part of an ontology of sorts, I prefer to think of them in terms of their utility to the users of Linguistics Stackexchange site.
As far as I know, there are two ways of using tags:
- Click on the tag to find all the questions tagged as such.
- Adding one or more tags to free-form words in the search field.
For either of these options, the existence of speech-rate seems pointless.
- There are just two questions with speed, indicating that this is not a topic in popular demand. IMO, if a tag is populated by extremely few questions, there is little reason for it to exist in the long term. New questions may be tagged with all kinds of new terms, but if after a couple of years, there are no more questions with that tag, the tag should be deleted. Just my 2¢.
- When looking for questions on speech rate, users can add these words to the query even if the tags did not exist.