Voynich decoded completely

[MarcoP]

If I were to assume a third, unknown language now, it would seem more like an excuse than a possibility.

As Rene and others said, there is no need to assume a specific language. In the last several decades, at least from Currier in the 70s to the recent Malta conference, properties that make Voynichese different from an ordinary written language have been pointed out (e.g. line-effects, consecutive similar words, word structure, low entropy, Feaster's positional patterns etc...). The task at hand is explaining those properties and anwering the question "why is Voynichese so different from any written language?". Some of the Malta papers focussed on this (e.g. the two by Gaskell and Bowern). Good answers that explain how Voynichese can be related with any underlying natural language will also work for other ordinary natural languages. Latin, German, Slovenian, Turkic, Hebrew, Italian, Romani, Farsi... it does not matter at this point.