I grew up with this series but I grew up with the Japanese version. Does anyone know if there a way to change the language? Thanks in advance.

There is a way to change the language. Be warned though, I have just started playing the game and there might be serious bugs later (I doubt it).

Here's what I had to do (Windows 10 pro):

1. back up your ***\Way of the Samurai 4\US folder
2. copy the contents of ***\Way of the Samurai 4\JP to ***\Way of the Samurai 4\US. Do not copy the sound folder, and I also did exclude UI\Texture and UI\Layout. I didn't do just a simple override, but moved the US subfolders and files into individual backup folders and the copied the japanese folders and files into the US folder. (otherwise I would get crashes).
3. Run as admin with WIndows 7 compatibility mode (otherwise there was no sound when playing in fullscreen mode and the game also crashed).

Some UI elements are not availlable in japanese (the files are missing), so you have to deal with very few english button prompts etc. but basically all the text (subtitles and dialog-texts, as well as your dialog choices) and maps are in japanese.

Another problem: I have found no way to enter a name for the player-character in any of the japanese scripts (neither hiragana, katakana nor kanji.)
By default your Samurai is named 無名侍. I guess the only way to change the name using kanji etc. would be to hex-edit the save-file.　(just tested it and it works - see screenshot)

you can read more about this here:
https://w.atwiki.jp/samuraidou4/pages/55.html

have fun!