Some other JS i18n frameworks:
http://airbnb.io/polyglot.js/
http://i18next.com/

Some links from Filip on Slack:

@jason @nielserik A little gold mine of practical tips on multilingual web interfaces and RTL support. BBC’s web team explaining how they tried to solve massive multilingual layouts and fonts http://responsivenews.co.uk/post/123104512468/13-tips-for-making-responsive-web-design - maybe it’s more relevant for the HTML person we might hire, but it will definitely affect a bunch of more technical things relating to templating engines, etc. I guess react will be a good helper when we get to that part. (edited)

(This also seems to contain some good tips in point #3 and #4 http://webdesign.tutsplus.com/articles/tips-for-designing-and-building-a-multilingual-website--cms-24708)

From rangle:

• format.js is definitely the right tool

• the react-intl components it provides should be used extensively

• 'ICU message syntax' it supports is known by translation firms eg. they can give translations in that format

• read the guides first before getting into the react components; the i18n guides