Ah I see I read what you said wrong. Any way I do not find where to edit the title of the tag cloud widget because when you use the widget it says no options for this widget.
If it requires you to edit files then it is not built in at least not in my opinion.
I was able to find a mod that did both I found random tag cloud to be able to change the widget name and I found hs tag cloud for the tag page.
I do wish both these mods were built in as that would be great.
Oops I used the word mods instead of plug in. To me they are the same thing as some scripts call them mods some adons and some plug ins.