I finally got that "mutan" means "mutant". Sorry about that.
Anyway, what you are saying is contradicting well established evidence.
Farnsworth's and Warden Vogel's comments on alien language 1 ("Alienese") being "impossible to translate" is what in the biz is known as a "joke", regardless of continuity.
In fact, "Leela's Homeworld" is the
first episode where characters actually engaged with the alien language.
In addition to that, you seem to refer to the language as the "mutant language", which also seems to disregard what Leela's mother, Munda, says, and I quote.
You won't pass for human, cutie. But if my PhD in exo-linguistics is worth diddly-poop, this note should convince them you're an alien.
In other words, that language was never used by mutants, Turanga Munda had apparently studied exo-linguistics (a pun on exoplanet, I guess), where she learnt how to write this alien language. In other words, it is actually a known language, but it is used so seldom, that most people simply cannot be bothered to know how to translate it.
If this language is really supposed to be an alien language 3, it is a very very terrible attempt at an additional language, as it is basically AL1 over again.