I know that languages change over time and they also diverge, which should decrease mutual intelligibility, but usually they do so in the way that keeps bunch of languages more or less together, while distancing them from their common ancestor.
It is easy to find facts like "bilingual dialog is generally possible in Scandinavian countries" and you can even get some precise numbers like "Italian has 89% similarity to French".
But its there a way to compare or test mutual intelligibility, to say, Italian and Latin (I know Italians generally can't read Latin, but they possibly also can't understand French)? Or can we say which language is closer to English, German or P. Germanic?
P.S. Actually, there was said "89% lexical similarity to French", I'm not sure what's the precise meaning.