In order to deploy the mobile language button at the top, we need to do some preparations.
Old bottom language button will be live with the new action bar and button at the same time for some time, so...
- Feature flag bottom language button (T140872)
- Feature flag action bar (stable HTML when disabled, beta action bar with language button at the top when enabled)
- Make sure the both JS & CSS related to this features will work when enabled but having old cached HTML
- Create followup task to remove cached HTML considerations (add FIXMEs with the task number) if necessary