I think we can began with globalization of templates, using nowadays tools as Wikidata, TemplateData, Wikimedia translation tolls an so on. Global repository can be the second step. Another option is procrastination.
Topic on Talk:Global templates/Proposed specification
Where would you store the code of the templates before there is a repository?
Test Wikipedia? Wikimedia Commons? Data in Wikidata for TemplateData? Mediawiki (Extension / Translation tool)? Any other suggestions?.
We must begin with the most used template in Wikipedia .
If you are trying to transclude a template into a page on the Spanish Wikipedia, and the template's code is stored on Test Wikipedia, Wikimedia Commons, Wikidata, or Mediawiki.org, it won't work. The code must be on the same wiki. That's why a repository is needed first.
We must broke up this Ouroboros. First a test site (it was offered a Wikipedia to test it). This can use *existing* tools in Wikidata and other Wikimedia projects (as translation tool) to support the globalization. I suggest beging with the most used template in Wikipedia, as an example /test that the idea works.
It can use Mediawiki extensions / repository or third party repository. When you wan use a template from this repository, you can download it to a local Wikipedia. This can be the first step for globalization (downloadization).