I see... well remember that the word filtering, in this case, is only done locally. Meaning: only you will see the changed text, your contacts will still see the original english text (unless, they too make a word filter for their own of course)
And even if something more customizable and something specific for this is added to Plus!, it will never be able to set what your contacts see, as your contacts have their own preferences; you can't force something upon your contacts without them having the ability to override it (eg: I bet you wouldn't like it either if a Chinees speaking person can change the stuff you see in Chinees
-no offence to chinees speaking people of course 
-).
/ 
