Just you asking this question I already know you won't like this series at all. It takes a lot of work and time to get into it. It has so much text and scenes it's hard for me to play and I usually can play anything.
First of all, yeah, the voices are japanese, but it's all translated. If you can handle reading subtitles the whole time, you'll be fine with the dialogue.
Second of all, you have to understand something. Yakuza's main focus is its slice of life characters. Yeah, the combat is a blast, but if you're like most who don't likereally well done slice of life settings, you might want to pass it up.
Oh, and prepare to read, A LOT! There's so much dialogue it's not even funny.
Just thought that I'd give you a heads up.
Project Beat a Game a Day, along with my Daily NES Archive: http://www.gamefaqs.com/boards/563947-a-view-to-a-kill