How can I manually upgrade translations?

quick-and-dirty hint to solve this problem:

1. find the function list_translation_updates() in wp-admin/update-core.php

   $updates = wp_get_translation_updates();
   if ( ! $updates )                  <- locate the if
   ...
   }
   else {                             <- add this
      print_r ( $updates );
   }
   

2. add the else-case and save the file

3. reload the dashboard page and you will get the desired information.