Well, some people do mumble. Mostly people under the age of 30. I have absolutely no problem hearing or understanding people who are older than that, but the young folks talk very fast, and usually too softly. I find myself saying, "What?" a lot when talking with them.
Same thing on TV. I really think the problem is the quality of TV sound, not my hearing. People reading or discussing the news, and older actors come through loud and clear. Younger actors, not so much. Fortunately, TV comes with closed captions. I wish people came with them as well. Maybe the words could be hovering in the air above their heads, while they mumble?
But it would probably be run by A-I, so there would be a lot of misunderstanding in the translation.