Duplicating site to 2nd Level Directory

Hello!

I’m working on a multi-site for a client and I’m looking to duplicate the sites I’ve already made so that the website can be viewed in different languages.

Primary domain: http://ironteam.hr/
Site 1: http://ironteam.hr/gym/
Site 2: http://ironteam.hr/project/
Site 3: http://ironteam.hr/en/

and I’m looking to also create the following:

Site 4: http://ironteam.hr/en/gym/
Site 5: http://ironteam.hr/en/project/

I have tried to duplicate using the plugin and I’m receiving the error message “Missing or invalid site address”. I understand that “Only lowercase letters (a-z) and numbers are allowed”, but I was wondering if there is a work-around that anyone can recommend?

Thanks in advance!

The page I need help with: [log in to see the link]