What makes it seem real is that in actual languages, letters and groups of letters appear with consistent frequencies, and the language in the Voynich manuscript has patterns you wouldn't find from a random letter generator.
Stvarnim se čini zato što se u stvarnim jezicima slova i skupine slova pojavljuju dosljednom učestalošću, a jezik iz Voynicheva rukopisa sadržava obrasce kakve ne može stvoriti nasumičan generator slova.