When multiple language packs are selected for installation, perform the installation asynchronously in the background via ad hoc task.
So admins can work out why the task might not be having an effect.
Similar to upgrade_language_pack(), update_langpacks_task should respect skiplangupgrade config. Also, this should be added to behat whitelist, so it can be disabled during on-sync period, when lang pack for master is not available.
Now langpacks will be updated by scheduled task every day rather than updating manually.