What’s the mechanism for magically understood speech from the monk’s Tongue of the Sun and Moon feature?

The rules for the monk ability Tongue of the Sun and Moon state:

Starting at 13th level, you learn to touch the ki of other minds so that you understand all spoken languages. Moreover, any creature that can understand a language can understand what you say.
PHB, pp.79

How does the meaning get transferred? Some possibilities I’ve thought of:

  1. The listener hears the words as the speaker forms them, and the meaning is sort of empathically transferred.
  2. The listener hears the words in a language he understands, Star Trek style, without hearing any of the actual mouth-sounds.
  3. When monk comes in contact with someone who speaks a language A, he rips the understanding of the language out of their mind and can thereafter actually speak A.
    • This is less likely, because it doesn’t say that he gains the new language, as such. However, perhaps he gains only the spoken language, and not the written part.
  4. The monk simply does understand all spoken languages after this level, and the bit about ki is just flavor text.

The first two answers imply that there needs to be another mind present who speaks A. The third implies that the monk at least needs to come across an A-speaker to understand it. The fourth implies that he can just speak and understand A upon leveling up.

I then have a follow up question, which might influence the way we think about the first one. The Magic Mouth spell (PHB pp.257) allows you to leave a message for others to hear, triggered by a circumstance of your choice. I think I’m in safe territory to say that the monk would definitely understand the message (“all spoken languages”). When the monk hears the message, how is he understanding it? The speaker’s mind isn’t there to be touched. Further, even if there’s some magic hoodoo going on there, what if (and please do forgive me for going outside the setting, but I couldn’t resist exploring the theory) he heard a radio, or a phonograph?

Along a similar vein, if (the gods only know why) you had a Monk 13/Wizard or Bard 3, and you cast Magic Mouth, could you specify that anyone hearing it would understand?

Summing up:

  1. How does the monk communicate meaning?
  2. Would the monk be able to understand a recorded message, where the one who left it might not even have a mind anymore?
  3. Can the monk leave a fully understandable message?

I also asked this related question about choosing who gets to understand the monk.