Game is about a Japanese conflict in Japan about Japanese people. Why would I want to play it in any other language?

Game is in 13th century Tsushima though, so they should speak like 13th century Tsushiman japanese people did, probably Late Middle Japanese. /s.

Which the Tsushiman dialect probably had a lot of korean elements to it at the time with its proximity.

Just saying modern japanese is vastly different to old japanese, and with the added bonus of the Tsushiman dialect being very different.

https://en.wikipedia.org/wiki/Late_Middle_Japanese 12th-17th century

https://en.wikipedia.org/wiki/Early_Modern_Japanese 17th-mid 19th century

and now Modern Japanese.

Yes, and the English that is spoken 700 years ago is quite different than what we use today. Why is expecting them to do that here any different? 

Point being it shouldn't matter whether it is in Modern English or Modern Japanese, neither would be authentic. Of course I understand preferences.

https://www.youtube.com/watch?v=ctlCwPg79dU

Microsofts - Loftis (on single player games):
"I don't think that it's dead per se,"
"I do think the economics of taking a single-player game and telling a very high fidelity multi-hour story get a little more complicated"

Sony - Shawn Layden (on single player games):
“My philosophy is to play to my strengths,”

“And if you look at the studios we have – Naughty Dog, Guerrilla, Santa Monica Studio, Japan Studio – that’s what we do well. We do story. We create characters.”

“Those are the kind of things we do well. It’s what we’re known for. It really speaks to our entertainment DNA. We wish to entertain. We wish to make you happy. We wish to make you cry. That whole range of emotions we can pluck at to make you have a great experience. We’re big on character. We’re big on story.”

Sony still believes in makeing Single player experiances, proof is in the pudding.

Super hyped for this, I have wanted a AAA set in Feudal Japan for many, many years. Figured it would be Ubisoft who finally gave us one, when they finally ran out of other settings for AC and had to give us AC Japan. Here's hoping it sells well enough to convince Ubisoft that there is demand for Feudal Japan games in the west, some AC directors have stated in interviews before that they didn't think there was enough demand in the west for Feudal Japan settings.