To what extent should the translation respect the grammar?

[Koen G]

In this case Marco was correct: what you gave us was not a sentence, since you had omitted essential parts. It's like if you give me a cow's tail and ask "is this a cow?", I would have to say "no". 

But there is a much bigger problem: what is grammatical in Greek, cannot be turned into English word by word and be grammatical as wel. Each language has its own rules for what is grammatical, hence the final sentence in English looks completely different.

And all of this is beside the point. If you think Voynichese is Greek, the true question is whether the Greek you produce is grammatical in Greek. The English translation of this Greek is irrelevant for the grammaticality question.

In summary, you gave us a bad English translation of an incomplete Greek sentence and asked if it was grammatical - there is no way for us to know. I think the bottom line is that if you want to be a translator, you first need to learn the language you are translating from (or be a native speaker).