In Henry V, Shakesperean English is difficult to understand (even for modern native English speakers -- at least for me) without a good amount of help.
However, there are a few scenes conducted mostly or entirely in French, and to my surprise, these scenes were perfectly readable with just a mild knowledge of modern French!
Why could this be? I have a few guesses, but I'm not impressed by any of them:
English has changed more in the time since Shakespeare than French.
Shakespeare's French was "easy" because he is a non-native speaker.
Written modern French reflects a much older version of the spoken language than the analogous situation for English.