fnando/i18n-js — pull request #173 by dmitrydims (2013-12-20 11:06:11+00:00)
Title: Rails 4: Fixed 'Uncaught SyntaxError: Unexpected token ILLEGAL'

Change related to the way Rails 4 encodes JSON. Long story short: now Rails doesn't escape unicode entities.
http://omegadelta.net/2013/04/28/changes-to-how-rails-3-2-13-and-4-0-encodes-unicode-in-json/