gettext.js provides a GNU gettext like interface for use in browsers, a MO file to JS transpiler and a webpack loader for MO files.
Full Docs: http://gettextjs.readthedocs.org/
import English from 'locales/en/LC_MESSAGES/messages.mo';
English.gettext('hello world');
English.ngettext('bug', 'bugs', 4);
import {gettext as _, ngettext, set_catalog} from "gettextjs";
set_catalog(...);
_("hello world");
ngettext("bug", "bugs", 4);
gettextjs <input> <output>
turns the input MO file int a JS file.