JS-driven popups, that's the visual layer, the data those popups present could be inside the
It is useful to give users a clue as to where they will be led to before they click through the title attribute; adding that same information in the middle of a paragraph could be a bit annoying if you have various links in an article.
The text inside the a tag sohould always be a clear indicator of the info behind that link, but it shouldn't be required to tell you if the destination is in Russian (pity
hreflang never caught on), an external site, a Google search, a link to all items on the current site tagged with international, a newspaper article... that is metadata that gives you a hint as to where you are being taken, but that does not need to visually pollute a paragraph.
Whether the average user is aware of tooltips, and can therefore enjoy the extra info on a link is a different question (bare in mind that average here shoudn't be taken statiscally since user savvyness is probably a Gauss dstribution, so the majority of your users is moderately savvy).
Semantically it makes sense, since you can then present it through js/css in any way you see fit. If you are going to add the same info in a, let's say
p, below the link, then the title attribute makes more sense since it is explicitly related to the link, unlike a p.
Once again, if people don't realize there is a tooltip, it may be worthless, but that is the visual layer, Where you hold the data is one thing, how you present it (relying on the default browser behaviour is a different thing).
EDIT: This is list of good examples of tooltips