Localizing possessives

I allow the player to choose his/her own name. I want to create a localized text that will create the possessive form of the name in C++. So, for example, if the name is FName MyName, and the value of MyName is set to “Susan” by the player, I want a widget to display “Susan’s sword.” I can append 's onto the MyName value, but that won’t localize. How do I create a localized version of “Susan’s”?