Fix credentials fallback language code

CHANGELOG.md

+- Role: credentials
+  - Set `LANGUAGE_COOKIE_NAME` so that Credentials will use the global language cookie.
+
 - Role: edxapp
   - Added `PASSWORD_POLICY_COMPLIANCE_ROLLOUT_CONFIG` to make configurable whether password complexity is checked on login and how such complexity is rolled out to users.
 

playbooks/roles/credentials/defaults/main.yml

@@ -50,7 +50,8 @@ CREDENTIALS_URL_ROOT: 'http://{{ CREDENTIALS_DOMAIN }}:{{ CREDENTIALS_NGINX_PORT
 CREDENTIALS_LOGOUT_URL: '{{ CREDENTIALS_URL_ROOT }}/logout/'
 
 CREDENTIALS_SECRET_KEY: 'SET-ME-TO-A-UNIQUE-LONG-RANDOM-STRING'
-CREDENTIALS_LANGUAGE_CODE: 'en_US.UTF-8'
+CREDENTIALS_LANGUAGE_CODE: 'en'
+CREDENTIALS_LANGUAGE_COOKIE_NAME: 'openedx-language-preference'
 
 # Used to automatically configure OAuth2 Client
 CREDENTIALS_SOCIAL_AUTH_EDX_OIDC_KEY: 'credentials-key'
@@ -147,6 +148,7 @@ credentials_service_config_overrides:
   CERTIFICATE_LANGUAGES: '{{ CREDENTIALS_CERTIFICATE_LANGUAGES }}'
   CREDENTIALS_SERVICE_USER: '{{ CREDENTIALS_SERVICE_USER }}'
   FILE_STORAGE_BACKEND: '{{ CREDENTIALS_FILE_STORAGE_BACKEND }}'
+  LANGUAGE_COOKIE_NAME: '{{ CREDENTIALS_LANGUAGE_COOKIE_NAME }}'
   CSRF_COOKIE_SECURE: "{{ CREDENTIALS_CSRF_COOKIE_SECURE }}"
 
 # See edx_django_service_automated_users for an example of what this should be