On pontoon.mozilla.org , we’ve recently migrated the Firefox, Thunderbird, and SeaMonkey localization repositories from hg to git. After this change, we have no projects using hg or svn as their repositories, and we have no projects using per-locale repositories (i.e. with {locale_code} in the repo URL).
We should probably drop support for these features, as they’re a source of unnecessary complexity and we currently can’t validate their behaviour in production. Mercurial (hg) repo support should probably be retained, as it’s pretty plausibly used by some third party.
Given that I’m currently working on a sync refactor, this change is liable to be made relatively soon. If you use Pontoon with per-locale repositories or svn, now would be a Really Good Time to speak up, preferably by replying to the GitHub issue on this.