Switch between live site and trial site

I am working on a client site that need to create French version of the current site. My plan is to duplicate the current site as a trial site, adding French content and restructure English pages. And use it as a preview site for client to review it. 

My question is - how can we turn off the current site, and point domain to new trial site by end of trial period? (Or if that is doable?)

If you have a different approach to adding a different language version of the site, please suggest here.

Thanks!