Summary: Upstream version of https://gerrit.wikimedia.org/r/c/phabricator/translations/+/1047593
Test Plan:
Set any languages and observe untranslated strings display proper PLURAL rules
With the downstream "translations" extension installed, set the language to traditional Chinese and see Simplified Chinese rather than English translations if they exist, like "Foo added/removed a project"
Reviewers: O1 Blessed Committers, avivey
Reviewed By: O1 Blessed Committers, avivey
Subscribers: avivey, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D25695
Summary: Ref T13395. Moves all remaining code in "libphutil/" into "arcanist/".
Test Plan: Ran various arc workflows, although this probably has some remaining rough edges.
Maniphest Tasks: T13395
Differential Revision: https://secure.phabricator.com/D20980
