Update client.de.yml

Updated it to sound more natural in German and corrected some errors

Can anyone tell me where "latest_by: "latest by"" is used? I can't find it.
Update client.de.yml

Changes in admin section
REFACTOR: moved the export.rake task into script/discourse script
FEATURE: add readonly mode CLI
PostsController refactoring.
Merge pull request #1991 from velesin/posts_controller_refactoring

PostsController refactoring.
FIX: broken 404 page. don't bother showing current_usre stuff
FIX: nuke spammer from flags page
FEATURE: Can select topics and hit `Dismiss Read` on the `/unread` filter
FEATURE: Bulk `reset read` status.
FEATURE: If you don't select any topics to "Dissmiss Read" it does all
by filter.
TRIVIAL: Move button to the bottom of the topic list
Remove old onebox fixtures
FIX: Amazon favicon was missing
FIX: undefined method error for some digests.
FEATURE: upload backups
simplify category definition copy
improved copy for watching/tracked adapted f/BBS
BUGFIX: Typo was causing dismiss read to use id = 0 instead of id = 1
add screenshots of live sites