Why can everyone understand each other?

[Warmmedown]

Is there any in-universe reason? Obviously the Nameks spoke and (at least in the past) wrote a language that was unintelligible to the earthlings.

 

[SIAD]

Apparently there is a Multiversal language (I mean a language in which all the characters in the Multiverse understand each other) and there are also their own languages (I mean depending on the sector where they live).

 

[Fantastische Hure]

Because their kimochis get through to each-other.

 

[Papasmurf]

So that AT doesn't need to invent more fictional languages than the one he is capable of creating