Forwarding if not exist

Hello,
I want forward all requests from

 https://www.businessnews.gr/*

to
https://www.businessnews.gr/el/*

but I want to bypass urls that are already in this form for example
https://www.businessnews.gr/el/rss
The above url I don’t want to be processed by the previous rules because it is going to be transformed to
https://www.businessnews.gr/el/el/rss

Is it possible?

Not possible with Page Rules, but you can do it with .htaccess (Google for .htaccess when a file doesn’t exist). Though I can only imagine it would go into a horrible loop when even the destination doesn’t exist.