I think having the Czech language spoken would be all right, but here I will speak about the English language version. Dan has said that Shakespearian English would not sound right because it does not have anything to do with his country where the game is set. Dan does not seem to want anything too regional either. Different ways of speaking bring different things to mind, and considerations should be made regarding this. If they all spoke Scottish English then it would sound like they were Scottish people speaking the language of foreigners, like people speaking a foreign language in their own accent, or like the language being spoken in a foreign accent. English spoken by Welshmen, Cornishmen and Irishmen are for the same reason off the list. They would bring to mind people speaking a foreign language in the accent of their own native language.
The goal would be to represent the native Czech speakers in the game who are not speaking a foreign language in an accent from another language, but their own language in its own accent(s).
I think it would be best to hire voice actors who are native speakers of English who speak some English accent or another, rather than a Scottish accent or an Indian accent or something like that.
So we have to ask which accent or accents would be best. The accents of Australia and New Zealand are English ones, but the trouble is what they bring to mind. They are sufficiently different to bring to mind the fact that they are the accents of colonies in a far away land. The Czech republic is not a colony in a far away continent, so Australian and New Zealand accents would not be suitable. In addition, the Australian accent is influenced by Irish accent, I have heard, and Irish accents in English have already been dismissed as too foreign to be good representations of the situation in Bohemia. American English, too, is a mixture of Irish and Scottish and the like, and is the distinctive sound of a colony on a far away continent. The Englishes of England itself are the best representations of the native accents of a native language, but there are so many how can we choose? Henry in the game is a peasant, and there are plenty more peasants too, so should we go for an old traditional accent from England for them? If so then we have to pick one of many old traditional modern Englishes. Over the centuries the different parts of England have come to speak so differently that a Dorset speaker and a Northumbrian speaker would be unable to understand each other (For those who don’t know, Dorset is in South-West England, with Northumbria being in North-East England). Another problem is that to the learned ear the birthplaces of the voice actors can be deduced, and having regional accents may be bad if someone says “aah, Henry’s from Dorset,” or “This person is from this particular street in Birmingham”. Also people who have learned English as a second language may have a hard time grasping what is being said if it is not spoken in the accent they are learning the language in or one like it.
Dan wants an international English. Fortunately, there has been an attempt at creating an accent that is understood throughout England, called posh or received pronunciation. The words are spoken quite clearly, although compared to some other native accents some vowels and consonants are dropped, and some words and grammar forms are missing. Although this accent is generally considered more Southern than Northern, it does not belong to any part of England in particular, making it the least regional accent of all of England, and it is widely understood and known. Those who speak it cannot have their birthplaces deduced.
Although I am proposing this widely spoken English as a good candidate, my personal preference is for a more traditional English, which would fit the theme of workers of the land in medieval Bohemia. I would quite like Shakespearian English too. I have read the English of the United States of America be proposed too, but for the following reasons I think it is a very bad choice. It is largely influenced by Irish speech and the like, so it sounds a lot like Irish English, so it sounds like it is spoken in a somewhat foreign accent. It sounds distinctively the speech of a a colony far away, nothing like Bohemia. Also something personal to me but also to some others in England, it sounds a bit silly and when I hear it I find it hard to take the speaker seriously. The USA didn’t even exist in the middle ages.
Having some in the game speak German and some Latin would be interesting, but many people playing the game may understand German or Latin, and understand things that Henry really shouldn’t. Maybe having an obscure Medieval German spoken could help with that.
Others, like Karel Roden, spent long years in Hollywood, and so did few others like Miroslav Taborsky or Barbora Kodetova I think. These three would be vital asset for Deliverance or any other game as well.