You mentioned emailing Sega about Yakuza 5 but do you happen to know their email? I’m searching the site and can’t find it but I did find a “Feedback and Opinion About a Game” section in their customer support. Do you think leaving feedback about the previous Yakuza games would help as well?

Couldn’t hurt!

They do mention that they read requests like that:

If you’d like to send us a message sharing your opinion about a game we’ve released, feel free to open a ticket and submit it.  We can’t always respond to these kinds of messages directly, but we do read them and gather the feedback for our development staff.  Additionally, you can go to the SEGA Forums and discuss your opinion of our games under the appropriate threads. Those threads are also monitored so we can take our customers’ feedback into consideration.

– Feedback and Opinion About a Game

Failing that, you could contact their PR guys:

https://twitter.com/kellieparker
https://twitter.com/RubyEclipse

or if you want to practice your Japanese you can try contacting Ryu Ga Gotoku Studio:
https://twitter.com/ryugagotoku

or Yakuza series producer Yokoyama Masa:
https://twitter.com/yokoyama_masa

or hit up Nagoshi on his blog:
http://www.ameblo.jp/nag0617 

Sega’s staff email usually goes firstname.lastname@sega.com so if you know the name of someone you’d like to get a hold of that should work.

If you want to contact Sony’s import localisation team try sending a tweet to http://twitter.com/giocorsi