How to change to the native voice pack with an english localization UI.
Tried playing the campaign but couldn't stand the abysmal voice acting?
Well here's how to fix it in 4 easy steps:

1. Head to the game directory which is commenly:
C:\Program Files (x86)\Steam\steamapps\common\Men of War

backup the file: localization.pak

(NOTE: switching launguage will require you to download 1.4GB as an update.)
2. right click on Man of War in your steam library, click properties, click on the Language tab, switch it to Russian.

3. Once updated copy localization.pak back to the games directory overwriting the existing file.

4. Now the movies, in-game cutscenes and narrative are in Russian
and the the menus, interface, item description, mission text are in English.
NOTE: the Russian pre rendered cutscenes don't have subtitles so if you want the rendered cutscenes back in english go to the game directory resource folder:
C:\Program Files (x86)\Steam\steamapps\common\Men of War\resource
delete video_rus.pak and rename video_eng.pak to video_rus.pak

All done! any problems do let me know below.

I don't take credit for all of this as most of this comes from buckybit guide over here: http://sp.zhabite.com/app/7830/discussions/0/846956740691053187/
and i just wanted to elaborate but the details about the videos in step 4 i found out myself.

Addendum:
I will try to unpack the video files of both the english and russian videos then use the english footage with russian audio and add in subtitles then repack it not entirely sure if that's possible but ill give it a shot in the near future.