I know that technically unicode and utf-8 are two different things, but more often than not the terms are used interchangeably (as UTF-8 is the de-facto standard Unicode file encoding). Should we merge the tags?
unicode-math ... but I think it would be ok to let utf-8 act as a synonym to unicode. This way these closely related subjects could be easier found in order to answer or to look-up.
Not a single utf-8 question has been tagged as unicode too, and the other way round. That's a sign for me that they are regarded as either being interchangeably or as unrelated - the latter is not the case. A misleading consequence is that unicode is not even mentioned in the list of related tags to utf-8, on the right sidebar, if you filter by utf-8! And the other way round as well - as if they were totally unrelated.
Update: I merged the tags and created an Unicode tag wiki.