ErrorDocument 404 /404.html
<IfModule mod_rewrite.c>
RewriteEngine on
# no RewriteCond => unconditionally rewritten
# If /de or /de/anything is requested, serve /, /anything.
# No further rule processing! (no / -> /en redirect)
RewriteRule ^de(.*)$ /$1 [END]
# NC => case insensitive regexp match ("nocase")
RewriteCond %{HTTP:Accept-Language} !^de [NC]
# L => last rule, no further processing
# R=302 => redirect, HTTP 302
RewriteRule ^$ /en [L,R=302]
</IfModule>
