Some internal templates are in English only. It would be important that they offer an option to use i18n, or fallback to a default value in English.

Examples:
The pagination template has several terms in English. This one is even more important, as it is an aria- element:

The disqus template "powered by" message is not i18n:

The rss template also has some sections only in English:

These are only some examples, there are others. There is need to find them, make a more complete list, then solve each of them. I believe this issue could be used to discuss how this will be approached.