Hello,
I had a similar problem because my site had the /en extension and I wanted to get rid of it. For some reason in the languages tab there were both USA english and GB english. (maybe because prestashop defaults to USA english from the initial install and I'm in the UK? Don't know).
Sorry to sound like a noob but the way I approached it was that I went to language settings and (localization -> languages) and I ticked on the 2nd language and disabled it. Then when i visited my site WITHOUT the /en extension it worked fine.
In regards to the redirect I don't think I'm going to worry about it too much as when people visit your site (store) they rarely, if never add the /en extention at the end. It is always with or without the "www".
Just my experience from it. Don't know if it helps... I am very new to prestashop.