Local creation of a tag on a Stack Exchange site requires a certain number of reputation points.
What about foreign/existing tags, i.e. tags which exist on other (or many) Stack Exchange sites? I feel the reputation required for creating those locally should be lower.
The immediate benefit is having more (relevant) tags on rather specialised questions which would otherwise have no or few tags, without adding to tag count chaos. The broader benefit would be that the various facets of a cross-cutting topic would be more easily discussed on multiple sites, while keeping track of what's going on.
As an example, we link MediaWiki-related questions from the official MediaWiki website and that allows watching multiple sites at once, but I feel there are some more, where the topic is being discussed, that we don't know of because of the lack of a local tag. And this is a rather specific topic; there are way more interdisciplinary ones.