How should languages work?

So I've been thinking about how languages should work. And I've come with two solutions: We either always point out when we switch from one language to another (which I don't prefer) or we color code the languages (which I prefer).

So each language would have its own color to show when the person switches from one language to another.
Example:

Thesnian (French)
Hurinan (German)
Regzan( Russian)
Mydarian (Latin)

Caplusan (Gaelic)

And how it would in a speech: ''Luigi, pass me the salt'' Mario said. ''Get it yourself, lazyass'' Luigi said back.

What do you guys think?