Fix setting of locale via routes mount ... defaults: { locale: :en } (

#923)

app/controllers/good_job/application_controller.rb

@@ -35,7 +35,9 @@ def switch_locale(&action)
     end
 
     def current_locale
-      if params[:locale]
+      if request.GET['locale']
+        request.GET['locale']
+      elsif params[:locale]
         params[:locale]
       elsif good_job_available_locales.exclude?(I18n.default_locale) && I18n.available_locales.include?(:en)
         :en

spec/app/controllers/good_job/application_controller_spec.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+require "rails_helper"
+
+RSpec.describe GoodJob::ApplicationController, type: :controller do
+  render_views # seems required for Rails HEAD
+
+  controller do
+    def index
+      render plain: "OK"
+    end
+  end
+
+  describe "#current_locale" do
+    it "defers to GET queries of params (to allow setting `mount...defaults: { locale: X })`" do
+      allow(controller.params).to receive(:[]).with(:locale).and_return(:en)
+      allow(controller.request.GET).to receive(:[]).with('locale').and_return(:de)
+
+      expect(controller.send(:current_locale)).to eq(:de)
+    end
+  end
+end