Where is Update translation? In admin/config/regional/translate/update I found the following message:

If there are available updates you can click on &quot;Update
translation&quot; for them to be downloaded and imported now or you can
edit the configuration for them to be updated automatically on the
Update settings page

The following screenshot reveals more:

I could not able to find Update translation anywhere. What is missing?
I suggest you the installation of Localization update module.

From the module's page:


  Automatically downloads and updates your translations by fetching them
  from localize.drupal.org or any other Localization server.


I use this module in all my projects, you can also have the .po files in the local server.