I try to look for the "flush" function and it's not on my theme. I'm using Blankslate with custom build css and html, so I didn't put it there by accident either. There are no other plugins activated... I haven't tried the solution on the http://wordpress.org/support/topic/home-page-shows-posts-in-both-languages-iis?replies=15 post yet.
Will look at this later this week. If by any chance you have another idea?
I'll try to install WP in a root directory and set it up the same to see if it'll work.