I didn't know they had namespaces/stacks of tags in EN at all, so thanks for your post. I've been sorting out my mountains of tags since earlier today with this and found a little bit of a method that helps. (Maybe this is how you do it already, but I'll post here just in case it helps);
in the left bar scroll to the tag you want to drag onto
click on 'tags' above the tag list on the left
it will open the tag search panel, find the tag you want to drag into the first one, and it'll pop up right beside it
Hope it's helps...
