Managed screenshots through the Amazon dev portal is quite painful. I'd like to offer some suggestions to the team.
1) When you add a localized media, it copies your default language media. You then have to go through and delete image one by one. This means click delete, then click confirm, then wait for the page to reload, then repeat. Quickest way to fix this is have a delete all button when in edit mode, delete all screenshots for the language at once.
2) Uploading is the most painful, you can only upload 1 screenshot at a time, you wait for it to upload then the page has to refresh before you can add the next screenshot. A bulk uploader here would be most welcome! :) (you can upload via sftp, but not sure about localized media)
Thanks :) Chris