Enable translations fallback (pupilfirst#825)

Translations fall back to `I18N_DEFAULT_LOCALE`, or `en` if the
environment variable is missing.

While we don't allow the user to select their locale (yet), we do have a
column in the database that's meant to enable this. There's no reason
to not use this value right now. At least it allows testing to make sure
that locales are working as they should.

app/controllers/application_controller.rb

@@ -10,6 +10,7 @@ class ApplicationController < ActionController::Base
   before_action :redirect_to_primary_domain, if: :domain_redirection_required?
 
   around_action :set_time_zone, if: :current_user
+  around_action :switch_locale, if: :current_user
 
   helper_method :avatar
   helper_method :current_host
@@ -40,7 +41,7 @@ class ApplicationController < ActionController::Base
   end
 
   rescue_from ActionController::InvalidAuthenticityToken do
-    flash[:error] =  I18n.t('shared.invalid_authenticity_token_error')
+    flash[:error] = I18n.t('shared.invalid_authenticity_token_error')
   end
 
   # Redirect all requests from unknown domains to service homepage.
@@ -66,48 +67,56 @@ def current_domain
 
   # Returns the "resolved" school for a request.
   def current_school
-    @current_school ||= if Rails.application.secrets.multitenancy
-      resolved_school = current_domain&.school
+    @current_school ||=
+      if Rails.application.secrets.multitenancy
+        resolved_school = current_domain&.school
 
-      raise RequestFromUnknownDomain if resolved_school.blank?
+        raise RequestFromUnknownDomain if resolved_school.blank?
 
-      resolved_school
-    else
-      School.first
-    end
+        resolved_school
+      else
+        School.first
+      end
   end
 
   def current_coach
     @current_coach ||= current_user&.faculty
   end
 
   def current_founder
-    @current_founder ||= begin
-      if current_user.present?
-        founder_id = read_cookie(:founder_id)
-
-        # Founders in current school for the user
-        founders = current_user.founders
-
-        # Try to select founder from value stored in cookie.
-        founder = founder_id.present? ? founders.not_dropped_out.find_by(id: founder_id) : nil
-
-        # Return selected founder, if any, or return the first founder (if any).
-        founder.presence || founders.not_dropped_out.first
+    @current_founder ||=
+      begin
+        if current_user.present?
+          founder_id = read_cookie(:founder_id)
+
+          # Founders in current school for the user
+          founders = current_user.founders
+
+          # Try to select founder from value stored in cookie.
+          founder =
+            if founder_id.present?
+              founders.not_dropped_out.find_by(id: founder_id)
+            else
+              nil
+            end
+
+          # Return selected founder, if any, or return the first founder (if any).
+          founder.presence || founders.not_dropped_out.first
+        end
       end
-    end
   end
 
   def current_startup
     @current_startup ||= current_founder&.startup
   end
 
   def current_school_admin
-    @current_school_admin ||= begin
-      if current_user.present? && current_school.present?
-        current_user.school_admin
+    @current_school_admin ||=
+      begin
+        if current_user.present? && current_school.present?
+          current_user.school_admin
+        end
       end
-    end
   end
 
   # sets a permanent signed cookie. Additional options such as :tld_length can be passed via the options_hash
@@ -137,7 +146,8 @@ def feature_enabled?(feature_name)
   # Makes redirects observable from integration tests.
   def observable_redirect_to(url)
     if Rails.env.test?
-      render plain: "If this wasn't an integration test, you'd be redirected to: #{url}"
+      render plain:
+               "If this wasn't an integration test, you'd be redirected to: #{url}"
     else
       redirect_to(url)
     end
@@ -156,18 +166,20 @@ def pundit_user
   helper_method :pundit_user
 
   def api_token
-    @api_token ||= begin
-      header = request.headers['Authorization']&.strip
+    @api_token ||=
+      begin
+        header = request.headers['Authorization']&.strip
 
-      # Authorization headers are of format "Authorization: <type> <credentials>".
-      # We only care about the supplied credentials.
-      header.split(' ')[-1] if header.present?
-    end
+        # Authorization headers are of format "Authorization: <type> <credentials>".
+        # We only care about the supplied credentials.
+        header.split(' ')[-1] if header.present?
+      end
   end
 
   def current_user
     if api_token.present?
-      @current_user ||= Users::FindByApiTokenService.new(api_token, current_school).find
+      @current_user ||=
+        Users::FindByApiTokenService.new(api_token, current_school).find
     else
       super
     end
@@ -179,6 +191,10 @@ def set_time_zone(&block) # rubocop:disable Naming/AccessorMethodName
     Time.use_zone(current_user.time_zone, &block)
   end
 
+  def switch_locale(&action)
+    I18n.with_locale(current_user.locale, &action)
+  end
+
   def sign_out_if_required
     service = ::Users::ManualSignOutService.new(self, current_user)
     service.sign_out_if_required
@@ -195,17 +211,28 @@ def authenticate_founder!
   end
 
   def storable_location?
-    non_html_response = destroy_user_session_path || (is_a?(::TargetsController) && params[:action] == "details_v2")
-    public_page = _process_action_callbacks.none? { |p| p.filter == :authenticate_user! }
+    non_html_response =
+      destroy_user_session_path ||
+        (is_a?(::TargetsController) && params[:action] == 'details_v2')
+
+    public_page =
+      _process_action_callbacks.none? { |p| p.filter == :authenticate_user! }
 
-    request.get? && is_navigational_format? && !request.xhr? && !public_page && !non_html_response
+    request.get? && is_navigational_format? && !request.xhr? && !public_page &&
+      !non_html_response
   end
 
   def store_user_location
     store_location_for(:user, request.fullpath)
   end
 
-  def avatar(name, founder: nil, faculty: nil, version: :mid, background_shape: :circle)
+  def avatar(
+    name,
+    founder: nil,
+    faculty: nil,
+    version: :mid,
+    background_shape: :circle
+  )
     if faculty.present? && faculty.image.attached?
       return helpers.image_tag(faculty.image).html_safe
     end
@@ -214,11 +241,14 @@ def avatar(name, founder: nil, faculty: nil, version: :mid, background_shape: :c
       return helpers.image_tag(founder.avatar_variant(version)).html_safe
     end
 
-    Scarf::InitialAvatar.new(
-      name,
-      font_family: ['Source Sans Pro', 'sans-serif'],
-      background_shape: background_shape
-    ).svg.html_safe
+    Scarf::InitialAvatar
+      .new(
+        name,
+        font_family: ['Source Sans Pro', 'sans-serif'],
+        background_shape: background_shape
+      )
+      .svg
+      .html_safe
   end
 
   def domain_redirection_required?

app/javascript/shared/i18n.js

@@ -2,7 +2,8 @@ import { I18n } from "i18n-js";
 import translations from "locales.json";
 
 export const i18n = new I18n(translations);
-i18n.locale = document.documentElement.lang || "en";
+
+i18n.enableFallback = true;
 i18n.missingTranslationPrefix = "Missing translation: ";
 
 global.i18n = i18n;

config/environments/production.rb

@@ -90,7 +90,7 @@
 
   # Enable locale fallbacks for I18n (makes lookups for any locale fall back to
   # the I18n.default_locale when a translation cannot be found).
-  config.i18n.fallbacks = [I18n.default_locale]
+  config.i18n.fallbacks = true
 
   # Send deprecation notices to registered listeners.
   config.active_support.deprecation = :notify

config/initializers/i18n.rb

@@ -6,5 +6,5 @@ def self.translations
   end
 end
 
-I18n.available_locales = ENV['I18N_AVAILABLE_LOCALES'].split(',')
-I18n.default_locale = ENV['I18N_DEFAULT_LOCALE']
+I18n.available_locales = ENV.fetch('I18N_AVAILABLE_LOCALES', 'en').split(',')
+I18n.default_locale = ENV.fetch('I18N_DEFAULT_LOCALE', 'en')