Update arcanist to work with more modular translations
Summary:
Ref T7152. Ref T1139.
- Tweak API.
- Move translations out of init file.
Test Plan:
- Ran arc.
- Added a goofy translation and made sure it was working.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Differential Revision: https://secure.phabricator.com/D11746