Putting the tale before the horse(man)
It is often wondered when writing historical fiction or Science fiction or even fantasy how much detail you include. This is one of those awkward questions where there is no definitive answer. rather the choice is the readers and dependent upon what they like. I agree with those that think that that voice should be authentic but I also agree that there can be no truly authentic voice (unless the history is very recent). My personal preference is for archaisms in historical fiction and science in Science Fiction to give a feel for the age.
But lets be honest we don't really know what language and expletives they would have used at Thermopylae or even Waterloo ( better chance). Recently in a magazine that I am involved with we printed the same story in two separate editions. Science fiction and so you may think not applicable but I think that it is. The first story was written in a popular thriller style, the second in a hard sci-fi format. The first easy to read and follow, the second full of scientific terminology, alien languages and thought patterns that were almost indecipherable. When asked to vote on which they preferred the 1,760 respondents voted almost fifty/fifty for each story. The Author, "Marie Mainsford" was astounded, expecting the "easy to read" thriller to win by a huge margin. I think what whilst there will always be those that enjoy the "easy" option that there are many others that wish their reading material to challenge them. They do not mind that it is difficult to read or if they have try to understand a difficult concept. On the contrary that just adds to the joy of the tale for them. I also suspect that it will ever be thus.