Build the locale path with an `_` instead of a `-`

The locale code is turned into an asset path with an underscore
instead of a dash.

The language codes are transformed by `I18n.locale` into a code with a
dash. But the resources for translating are always stored in a path
using a `_` separating the language and the region code.

app/helpers/application_helper.rb

@@ -309,4 +309,8 @@ module ApplicationHelper
   def show_new_repo?
     cookies["new_repo"] == "true" && body_data_page != 'projects:show'
   end
+
+  def locale_path
+    asset_path("locale/#{Gitlab::I18n.locale}/app.js")
+  end
 end

app/views/layouts/_head.html.haml

@@ -37,7 +37,7 @@
   - if content_for?(:library_javascripts)
     = yield :library_javascripts
-  = javascript_include_tag asset_path("locale/#{I18n.locale.to_s || I18n.default_locale.to_s}/app.js") unless I18n.locale == :en
+  = javascript_include_tag locale_path unless I18n.locale == :en
   = webpack_bundle_tag "webpack_runtime"
   = webpack_bundle_tag "common"
   = webpack_bundle_tag "main"

changelogs/unreleased/bvl-fix-locale-path.yml

+---
+title: Correctly render asset path for locales with a region
+merge_request: 14924
+author:
+type: fixed

spec/helpers/application_helper_spec.rb

@@ -309,4 +309,12 @@ describe ApplicationHelper do
       end
     end
   end
+
+  describe '#locale_path' do
+    it 'returns the locale path with an `_`' do
+      Gitlab::I18n.locale = 'pt-BR'
+
+      expect(helper.locale_path).to include('assets/locale/pt_BR/app')
+    end
+  end
 end