Capcom are still undecided whether to release Monster Hunter Tri G in the West. In a recent Q&A session with investors, they answered whether or not there is any plans:
Q What are your overseas plans for “Monster Hunter 3 (Tri) G”?
A Our stance for the overseas distribution of this title is the same as for the entire “Monster Hunter” series. We are selling the preceding title “Monster Hunter Tri” overseas so we will consider launching this title overseas, too. But no decision has been reached yet.