How to know if a language is constructed or natural?

Question

Imagine you get access to a rather long book for which the following is true:

• It is written in an unknown language with an unknown script.
• We can't rely for whatever reason on the fact that the language of the book is not in Ethnologue.
• The book came with no translation, and no known dictionary of the language exists.

Given all the above is there a way to say if the language of the book natural or constructed? How should one approach determining this based only on the content of the book?

Answer 1

Unknown language and unknown script is a very hard combination to draw any conclusions. Even with a substantial amount of text we are usually lost in making sense of that.

Things become a little bit better when we have some clues on the script like

• words are separated somehow
• we know the principle of the script (alphabetic, syllabary, ideographic)

In this case we can try some statistical methods on things like word frequency and word length (does the language follow Zipf's law?), trying to identify morphemes, especially inflectional ones, trying to infer syntactical features, and compare that to natural languages.

But, unless the language is very schematic and unnatural in its construction, we will probably be unable to give a decisive answer to the question natural or constructed.