i think you cannot, because there may be incompatibilities you have to translate everything in its entirety with the same translator If you take the MTL version you have this thread, you have to translate it with sugoi if you use gpt you will probably have to translate the base game and the expansion, Because if you do what you say, it's more about programming than translating. Furthermore, you don't know how two different translation systems are going to behave in the same game.
I have not heard of any case of a game having different mtl together in a single game. Although it is an expansion, it is part of the game and probably has common events and more shared files that need to be overwritten.