It means Congregation of the Mission - it is an institute of priests and brothers of the Catholic church, belonging to a particular order I believe, though I'm not sure. "I'll be hanged if I'm going to A" - it is a colorful expression meaning that there is no possible way that A is going to happen, if I can help it. It doesn't mean that I'll actually be hanged - I might feel angry or very bad, but death is not a possibility. "I'll be hanged if I'm going to that party with him" - There is no way that I'll go to that party with him.

According to this website: http://www.catholicdoors.com/misc/abbrev.htm There are three options, C.M. Carmelite Missionaries, India C.M. Congregation of the Mission, India C.M. Congregation of the Mission (Vincentians or Lazarists) Since your priest is in the US, the third option is probably correct. A Catholic order is a group of people or a specific community. A congregation is an assembly of people (at a church) or a group of Catholics who are under a common leader or rule. A mission is a group of Catholics who are in a (foreign) country to try to spread their religion. There might not be a good translation of C.M. into Chinese. You might just want to omit C.M. in your translation since "priest" covers his profession adequately. I think very few non-Catholic Americans would know what C.M. means. "I’ll be hanged if I'm going to miss this chance." This means, "I will really regret it (or I will really hate it) if I miss this chance."