Maybe this is a little
what with me being English AND not exactly answering your main question, but:
With other companies, it usually depends where the greatest market is. Which of course is America or Japan (this applies mainly to consoles, but PC games to a certain extent). Europeans rarely get their own anything, which is actually fine with me because I love communities and forums with lots of different nationalities. Opens debate somewhat to see varying points of view (P.O.V) and tastes... perhaps even cultural things to some degree.
With that said, perhaps it helps Larian for all players to be in one major place, so they don't have to go to 6-8 different forums (one for each nationality of players perhaps) just to see our views and reactions? It's hard enough for me to browse these forums already, I want to play and there are over six I 'lurk' through daily. (including DD). Maybe Larian would rather spend their time fixing bugs/supporting DD & BD than browsing these forums. I know I would.
I know it's nice to have a 'home-grown' developer... Britain has/had a few Bullfrog (R.I.P), Rockstar North (GTA games), Rare, Codemasters etc. Of which most (not all) target the American market first (Release games there first etc) because it's the more profitable market. Games are more popular over there. Money makes the world go round.
I understand your point though, if Larian were a British company and their forum was only in Dutch, i'd be a bit
because i'm rubbish and only speak one language.
( sorry if that was a bit off topic )