Some cryptographic codes are akin to inventing one's own secret language, along with new words, new expressions, and new grammar. I'll refer to these strong codes as "secret languages". Note that when all speakers of an ancient language dies, it becomes a secret language.
It seems to me that cracking secret languages is beyond the realms of cryptanalysis. After extensive search, I haven't found a single secret language that was ever cracked without any known plaintexts such as finding available translations. Are there any ways to crack or even crypto-analyze secret languages only using raw text written in that secret language? It is obviously possible with ciphers because they operate on the syntax level, but secret languages operate on abstractions and high-level meanings.
If the answer is yes, then why is cracking some ancient secret languages is a really hard thing to do unless one finds a translation? I challenge you to crack the The Na'vi language only by reading excerpts written in Na'vi. Also, can you point to one example of a secret language that was cracked only by looking at the text of that language?
If the answer is no, why isn't this used in modern computer cryptography? I presume it's because computers have a hard time manipulating meanings, abstractions and grammar and are better suited for manipulating syntax, letters and bits, and hence only ciphers are practical. But any more info would be appreciated.
A similar question was asked here but the two answers were contradictory, and it was closed, probably because it was focused on ancient languages and was considered a history question.