Is there any protocols to identify what sort of document MS-408 is?

[Rafal]

I don't know what the entropies of actual conlangs are

Esperanto will be probably very similar to Latin or Italian. Any constructed language based on one or more real languages ( so called a posteriori conlang) will have have similar statistical properties to the real languages being the inspiration.

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On the other hand there are some really weird constructed languages which may behave differently, for example:

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But yet on the another hand any "weird" constructed language, strongly different from natural languages, would be quite anachronistic for the 1400s.