Locale zh_CN is not applied to Devise::SessionsController

Summary

Default locale is not set to zh_CN for the controllers which do not inherit from ApplicationController.

Known Controller List without zh_CN

1. SessionsController < Devise::SessionsController
2. TODO

Steps to reproduce

1. Goto login page
2. Fill with a wrong username
3. Expect the error message is in zh_CN

Example Project

What is the current bug behavior?

What is the expected correct behavior?

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes