In this case there is no difference whatsoever. Colloquially we say: I want to be an interpreter. I hope one day to possess the skills to be an interpreter. When you have finished becoming an interpreter, it means you ARE an interpreter.

to be means that you are in a current state/position. to become means that you still need to get there. you can say: i hope to be an interpreter someday. so you hope to be in this state/position someday. "I hope one day I will possess the skills to become an interpreter." means that you still need to obtain those skills in order to become an interpreter. i hope that made sense..

become.