Adding directory to url with htaccess & rewrite - apache

Question

I have a site based on Modx CMS and I need to create a 301 redirect for the main folder & old links after the multilanguage functionality has been enabled.
What I need to achieve is the default fallback to english eg. make sure that:
example.com/products -> example.com/en/products
example.com/about - example.com/en/about
etc.
I also need to make sure that if there already is a language selection (for example de) in the url, I don't add en to url. (so no example.com/en/de/products)
I am having trouble adding the /en/ to url and I am ending up with infite /en/en/en loops on the URL
To add the /en/ to the url I tried the following.
RewriteCond %{REQUEST_URI} !^/de$
RewriteCond %{HTTP_HOST} .*example.com [NC]
RewriteRule ^https://example.com/en/%{REQUEST_URI} [L,R=301]
It results to a endless /en/en/en loop in the url.
The whole htaccess is as follow:
RewriteEngine On
RewriteCond %{HTTPS} !=on
RewriteRule ^.*$ https://%{SERVER_NAME}%{REQUEST_URI} [R,L]
RewriteBase /
RewriteCond %{REQUEST_URI} !^/de$
RewriteCond %{HTTP_HOST} .*example.com [NC]
RewriteRule ^https://example.com/en/%{REQUEST_URI} [L,R=301]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?q=$1 [L,QSA]

Answer 1

Try the code below. The rules are chained (the default is AND). So, if your URL doesn't start with /en, /de, it's not the index (/), and it's not a file name or a directory, do a 301 redirect to the English version:
RewriteEngine On
RewriteCond %{REQUEST_URI} !^/en
RewriteCond %{REQUEST_URI} !^/de
RewriteCond %{REQUEST_URI} !^/$
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^ https://%{HTTP_HOST}/en%{REQUEST_URI} [L,R=301]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?q=$1 [L,QSA]