Bugfix: Always use the default language when generating emails.

app/controllers/application_controller.rb

@@ -275,11 +275,7 @@ class ApplicationController < ActionController::Base
     request.base_url
   end
 
-  def set_locale
-    Gitlab::I18n.set_locale(current_user)
-
-    yield
-  ensure
-    Gitlab::I18n.reset_locale
+  def set_locale(&block)
+    Gitlab::I18n.with_user_locale(current_user, &block)
   end
 end

app/mailers/base_mailer.rb

 class BaseMailer < ActionMailer::Base
+  around_action :render_with_default_locale
+
   helper ApplicationHelper
   helper MarkupHelper
 
@@ -14,6 +16,10 @@ class BaseMailer < ActionMailer::Base
 
   private
 
+  def render_with_default_locale(&block)
+    Gitlab::I18n.with_default_locale(&block)
+  end
+
   def default_sender_address
     address = Mail::Address.new(Gitlab.config.gitlab.email_from)
     address.display_name = Gitlab.config.gitlab.email_display_name

config/initializers/fast_gettext.rb

 FastGettext.add_text_domain 'gitlab', path: File.join(Rails.root, 'locale'), type: :po
 FastGettext.default_text_domain = 'gitlab'
 FastGettext.default_available_locales = Gitlab::I18n.available_locales
+FastGettext.default_locale = :en
 
 I18n.available_locales = Gitlab::I18n.available_locales

lib/api/api.rb

@@ -45,9 +45,9 @@ module API
     end
 
     before { allow_access_with_scope :api }
-    before { Gitlab::I18n.set_locale(current_user) }
+    before { Gitlab::I18n.locale = current_user&.preferred_language }
 
-    after { Gitlab::I18n.reset_locale }
+    after { Gitlab::I18n.use_default_locale }
 
     rescue_from Gitlab::Access::AccessDeniedError do
       rack_response({ 'message' => '403 Forbidden' }.to_json, 403)

lib/gitlab/i18n.rb

@@ -12,15 +12,36 @@ module Gitlab
       AVAILABLE_LANGUAGES.keys
     end
 
-    def set_locale(current_user)
-      requested_locale = current_user&.preferred_language || ::I18n.default_locale
-      locale = FastGettext.set_locale(requested_locale)
-      ::I18n.locale = locale
+    def locale
+      FastGettext.locale
     end
 
-    def reset_locale
+    def locale=(locale_string)
+      requested_locale = locale_string || ::I18n.default_locale
+      new_locale = FastGettext.set_locale(requested_locale)
+      ::I18n.locale = new_locale
+    end
+
+    def use_default_locale
       FastGettext.set_locale(::I18n.default_locale)
       ::I18n.locale = ::I18n.default_locale
     end
+
+    def with_locale(locale_string)
+      original_locale = locale
+
+      self.locale = locale_string
+      yield
+    ensure
+      self.locale = original_locale
+    end
+
+    def with_user_locale(user, &block)
+      with_locale(user&.preferred_language, &block)
+    end
+
+    def with_default_locale(&block)
+      with_locale(::I18n.default_locale, &block)
+    end
   end
 end

spec/lib/gitlab/i18n_spec.rb

 require 'spec_helper'
 
-module Gitlab
-  describe I18n, lib: true do
-    let(:user) { create(:user, preferred_language: 'es') }
+describe Gitlab::I18n, lib: true do
+  let(:user) { create(:user, preferred_language: 'es') }
 
-    describe '.set_locale' do
-      it 'sets the locale based on current user preferred language' do
-        Gitlab::I18n.set_locale(user)
+  describe '.locale=' do
+    after { described_class.use_default_locale }
 
-        expect(FastGettext.locale).to eq('es')
-        expect(::I18n.locale).to eq(:es)
-      end
+    it 'sets the locale based on current user preferred language' do
+      described_class.locale = user.preferred_language
+
+      expect(FastGettext.locale).to eq('es')
+      expect(::I18n.locale).to eq(:es)
     end
+  end
 
-    describe '.reset_locale' do
-      it 'resets the locale to the default language' do
-        Gitlab::I18n.set_locale(user)
+  describe '.use_default_locale' do
+    it 'resets the locale to the default language' do
+      described_class.locale = user.preferred_language
 
-        Gitlab::I18n.reset_locale
+      described_class.use_default_locale
 
-        expect(FastGettext.locale).to eq('en')
-        expect(::I18n.locale).to eq(:en)
-      end
+      expect(FastGettext.locale).to eq('en')
+      expect(::I18n.locale).to eq(:en)
     end
   end
 end

spec/mailers/notify_spec.rb

@@ -128,6 +128,15 @@ describe Notify do
               is_expected.to have_body_text(namespace_project_issue_path(project.namespace, project, issue))
             end
           end
+
+          context 'with a preferred language' do
+            before { Gitlab::I18n.locale = :es }
+            after { Gitlab::I18n.use_default_locale }
+
+            it 'always generates the email using the default language' do
+              is_expected.to have_body_text('foo, bar, and baz')
+            end
+          end
         end
 
         describe 'status changed' do