I don't recall them saying anything about him losing the ability to understand other pokemon. So if the writers wanted to pull this off, it's not like they couldn't, even if they haven't done it before.Has Rotom ever translated pokemon speech? Its always seemed like it lost the ability to understand other pokemon when it became the Rotom dex. Heck, it itself rarely even speaks as if it is a pokemon, even though other characters refer to it as one.
That's not really what i wanted though. I just want the totem battles to last longer than 7~8 min, but apparently that would be awful because there'd be no dialogue.