www.example.com - DE version
www.example.com/de - DE version
www.example.com/en - EN version

www.example.com - DE version
www.example.com/de ---> Redirect 301 to www.site.com
www.example.com/en - EN version

RewriteEngine on
RewriteCond %{HTTP_HOST} !^www.
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]

RewriteRule ^(?:de|de/(.*))$ /$1 [R=301,L]