Well Beowulf was 8th to 11th century, so again that's 200 years before our game takes place. Beowulf is also English, remember this game takes place in Bohemia, different culture, and language.
It still has to be extra time though, time that could be spent on the important features, instead of a unnecessary profanity filter.
Where i come from everyone swears on a regular basis. Adults, children, old people. I can't imagine it being much different in other countries. These people are also peasants, they weren't proper and refined people. Henry (the mc) is also a solider, ive met plenty of vets and they don't have clean mouths, i can't imagine this being different in 1403.
Because there is no point. This is going to be an M rated game with violence, and there will be some sex. What makes profanity any worse than either of those? Games like Call of duty have a younger fan base, and there fore they have to put profanity filters in to shut up the parents who ignore ESRB ratings.
It's just a waste of time and money, people who find profanity immoral, or unpleasant probably won't like the rest of the content in this game.