Redirect pages under the folder DE to DE-DE

Why is this change being made?

closes #11262 (closed)

In order to facilitate the Smartling transition and new URL strategies for localization, this issue will move any files and directories under the /DE/ folder to be in the /DE-DE/ folder.

• Relevant pages have been moved.
• The pages still function as intended after being moved.
• Relevant canonical URLs have been updated (if any).
• Redirect rules have been created.
• The redirect works as intended in production (don't forget to verify after release).