See title.
[unicode] seems to be more popular at the moment.
If there's any reason against -- there might be questions about utf8 encoding in particular but that seems rather unusual and utf8 is default encoding anyway. And we don't have dependent tag for now Could we make tags imply other tags?
(I don't have enough score to suggest synonym myself)
utf8
tagged ones toutf-8
which since the referenced post is a synonym forunicode