Make it easy to use translation strings from JavaScript

[hubertlepicki]

I think the Translator should provide and API, that would allow fetching the translations to JavaScript and mobile clients.

We have a valid use case in project me, Iryna and Marcin work on at the moment, where we have custom API endpoint that outputs all the translations to JSON, to format easily usable with angular-translate library (https://github.com/angular-translate/angular-translate).

The implementation in the translator could be very similar. But I think the request should specify what locales we want to fetch, i.e. do not output all available locales at once (too many), and have endpoint like /translations/en.json or something that would fetch only those locale that are needed.

[hubertlepicki]

In one of the projects, we're using this code:

    I18n.t("hello") # trigger loading of translations

    keys = Translator.keys_for_strings
    @translations = Hash[keys.map { |key|
        [
          key,
          begin I18n.t key; rescue; end
        ]
      }].to_json
  end

to generate the list of translations to be rendered in json format