TLDR: Templates can now use datasets on Commons for all their localizable messages, making it possible to copy/paste templates between wiki without any changes.
If you look at the Graph:Lines template [1], there is a small link under each graph that points to the data source. That link is automatically localized on enwiki and ruwiki because the actual messages are stored in a Commons' Dataset, while the template itself is identical on both wikis.
The magic happens in the Module:TNT (hoping it won't blow up):
*{{#invoke:TNT | msg | DatasetDict.tab | message-key | param1 | param2 | ... }}*
I would love to support template doc pages too, but I'm not sure how well VE and other tools will work with the <templatedata>
This is an experimental thing, just hacking on it in my free time, and would love to get your feedback on the viability of this approach. Thanks!
Links: enwiki: https://en.wikipedia.org/wiki/Template:Graph:Lines ruwiki: https://ru.wikipedia.org/wiki/Template:Graph:Lines TNT: https://commons.wikimedia.org/wiki/Module:TNT Dictionary: https://commons.wikimedia.org/wiki/Data:Original/Template:Graph:Lines.tab