Your very observant, yes we did recently make this change redirecting, but to answer the question posed in the subject header, the forum is open to worldwide users, but is currently only being linked to from certain countries.
This is done because StarTrekMovie.com is being used globally and we want to make sure people in worldwide countries get the local version of the site.
You can always get to the forums by going to http://www.startrekmovie.com/forums/
globally (only the root domain and index page cause this redirect), but I will mention the issue about linking to the forums on the international sites to that team. Thanks for bringing it up!