Language redirect via .htaccess

.htaccess

### BEGIN Language redirect

## Example:
# - root URL: http://www.example.com/
# - DE version: http://www.example.com/de/
# - EN version: http://www.example.com/en/
# - IT version: http://www.example.com/it/

## Further notes
# Works also for websites with site root in subdirectory, eg. http://www.example.com/blog/
# Works with both HTTP and HTTPS automatically, eg. https://www.example.com/
# Order of language preference is: DE, EN, IT - it can be changed by reordering (de|en|it) regex below.
# DE is default language for users who speak neither DE, EN nor IT.

# Tell bots, that the content is based on language
<IfModule mod_headers.c>
  Header append Vary Accept-Language
</IfModule>

<IfModule mod_rewrite.c>
  # Store the current working (sub)directory and request URI.
  # Examples:
  # http://www.example.com/some/path/ => CWD is empty ; CRU = /some/path/
  # http://www.example.com/blog/some/path/ => CWD = /blog ; CRU = /some/path/
  # http://www.example.com/blog => CWD = /blog ; CRU = /
  RewriteCond /$0#%{REQUEST_URI} ([^#]*)#(.*)\1$
  RewriteRule ^.*$ - [E=CWD:%2]
  # Store the current request uri without any subdirectory.
  RewriteCond /$0#%{REQUEST_URI} ([^#]*)#(.*)\1$
  RewriteRule ^.*$ - [E=CRU:%1]

  # Set environment variable of current scheme for later usage via %{ENV:PROTO}.
  RewriteRule ^ - [E=PROTO:http]
  RewriteCond %{HTTPS} =on [OR]
  RewriteCond %{ENV:HTTPS} =on
  RewriteRule ^ - [E=PROTO:https]

  # If user prefers one of existing languages, redirect properly...
  RewriteCond %{ENV:CRU} ^/$ [NC]
  RewriteCond %{QUERY_STRING} ^$ [NC]
  RewriteCond %{HTTP:Accept-Language} (de|en|it) [NC]
  RewriteRule ^$ %{ENV:PROTO}://%{HTTP_HOST}%{ENV:CWD}/%1/ [L,R=302]
  # ...redirect all other languages or "no language" to German version.
  RewriteCond %{ENV:CRU} ^/$ [NC]
  RewriteCond %{QUERY_STRING} ^$ [NC]
  RewriteRule ^$ %{ENV:PROTO}://%{HTTP_HOST}%{ENV:CWD}/de/ [L,R=302]
</IfModule>
### END Language redirect