This addon adds hierarchical tags to the browser in Anki. The addon is published on Ankiweb.
To create hierarchies use double-colons in the tag names, for example "learning::anki" or "language::japanese".
This addon is licensed under the same license as Anki itself (GNU Affero General Public License 3).
When clicking on a tag in the hierarchy, an asterisk is added to the search term. The effect of that is that all notes with that tag and all subtags are searched for.
But a side-effect is, that all tags with the same prefix are matched. For
example if you have a tag it and a tag italian, clicking on the tag
it would also show content from italian. Let me know if this affects
you and I'll try to work around this.
The add-on was written by Patrice Neff. I try to monitor threads in the Anki Support forum. To be safe you may also want to open a ticket on the plugin's GitHub issues page.