I18n.locale getting reset to :en in between controller and the view - ruby-on-rails

Question

I'm trying to internationalize a Rails/Spree app using spree's own spree_i18n gem, but I can't get it to work.
I made a minimal app which recreates the problem here.
To cut a long story short, I have the following code in my ApplicationController:
before_action :set_locale
def set_locale
I18n.locale = params[:locale] || I18n.default_locale
puts I18n.locale
end
And code in my view which should be translated (<%= t("whatever") %>). But no matter what I do, the text is always output in English.
With some additional code for debugging, I can see that once set_locale is called but while execution is still within the controller, the locale is correct (e.g. if I visit the url /?locale=es, then the puts statement in the above controller code outputs es).
But by the time execution has reached the view, the locale has somehow been reset to en. (E.g. adding <% raise I18n.locale.to_s %> within the view raises "en" as an error message.)
I've opened an issue on Spree's Github because as far as I can tell I've followed their instructions exactly and it's still not working, but I may still be missing something. Why isn't the locale getting set properly?
(Note: I should add that the Spree.t doesn't work either, not just t.)
EDIT: If you look at the comment on my Github issue, you'll see that I got it working. However, I'm 99% sure that my solution is a hack and there's a better method I should be using. Bounty goes to whoever can tell me what I'm dong wrong.

Answer 1

Spree I18n gives a way to set default language: on config/application.rb with
config.i18n.default_locale = :es
And the possibility of setting the languages to be changed. Perhaps on config/initializers/spree_i18n.rb
SpreeI18n::Config.available_locales = [:en, :es, :de]
SpreeI18n::Config.supported_locales = [:en, :es, :de]
After that, you can remove set_locale on ApplicationController, because it has no effect.
With this at place, it works like a charm.
Edited:
I change the message of error because I want to be sure that it works:
<%= product_description(#product) rescue Spree.t(:product_has_no_description) +
' ' + Spree.t(:action) %>
And I add a new product without description. Running the server at localhost
In english I see: "This product has no description Action"
In spanish I see: "Este producto no tiene descripción Acción"
In deutsch I see: "Produkt hat keine Beschreibung Aktion"
Exactly the expected.
You can see the source with changes at github

Answer 2

It is unclear to me how Spree handles localization and in your routes.rb you only mounts engine.
Basically you should start localize your app within routes.rb by adding:
scope "(:locale)", locale: /#{I18n.available_locales.join("|")}/ do
# routing and engines go here
end
Now, you need to keep your params[:locale] across requests, so add to app controller:
def default_url_options(options={})
logger.debug "default_url_options is passed options: #{options.inspect}\n"
{ locale: I18n.locale }
end
Last, detect and set locale for current request, depending on your input data:
before_filter :set_locale
def set_locale
if defined?(params) && params[:locale]
I18n.locale = params[:locale]
elsif current_user && current_user.language_id.present?
I18n.locale = current_user.language.code
elsif defined?(request)
I18n.locale = extract_locale_from_accept_language_header
end
I18n.locale ||= I18n.default_locale
I18n.locale = :en unless valid_languages.include?(I18n.locale.to_sym)
end

Answer 3

You may be using/setting the following in app/controllers/application_controller.rb, which doesn't work:
before_action :set_locale
def set_locale
I18n.locale =
Spree::Frontend::Config[:locale] =
Spree::Backend::Config[:locale] = :LOCALE
end
In core/lib/spree/core/controller_helpers/common.rb there is another before_filter called set_user_language. That filter gets called and re-sets the locale to the value of session[:locale], or if that's not defined it uses default locale.
To solve the issue, set session[:locale] = :LOCALE in your before_filter.