Resolve startup warning "application.langs is deprecated, use play.i18n.langs instead"

The application.conf has `application.langs="en,af,fr,es"` causing this warning:

> 23:07:06.197 WARN  [][application-akka.actor.default-dispatcher-5][play.api.i18n.Lang] - application.langs is deprecated, use play.i18n.langs instead

I'm not aware of any localized code on the backend side but this is the migration guide <https://www.playframework.com/documentation/2.9.x/MessagesMigration26>

