Reachmahjong.com

Sleeping Dogs is a new GTA-style free-roam action game where you play as an undercover cop infiltrating the triads of Hong Kong. There's a large immersive game world, engaging storyline, excellent martial arts combat, driving, shooting, loads of side-missions, unlocks, minigames and collectibles. You can watch an official trailer here: http://youtu.be/8QuIovDO6TE

There are some similarities to the games of the Yakuza series (developed in Japan) but sadly one area where Sleeping Dogs (developed in Canada) falls down is mahjong. They like to mention it occasionally to add a little oriental flavour ("go and collect her mahjong debts") but when you find people playing in public it looks like this - two players, hands on the empty sides and missing about a hundred tiles.
There is a mahjong minigame available to play but sadly it's just poker with mahjong tiles (pinzu suit, 1-6 only, several of each).
By all means buy the game - it's great - but don't buy it expecting proper HK mahjong.

Oh, yeah, I bought it, its a good game, it´s very fun and have some interesting points. I don´t like this game has no real mahjong in it though...

It's like a hobo-version of Yakuza.

With regards to mahjong at least, yes!

I actually saw an interview where one of the developers/producers was asked about the absence of true mahjong in Sleeping Dogs and he said that it was so complicated that it would need to be made as a separate mahjong game release. Of course the Yakuza series manages to include mahjong with the full Japanese rules (along with shōgi and two hanafuda minigames) but their core market is Japan where a significant proportion of gamers know mahjong and are happy to play it. In the West sadly few people know the rules or want to learn them and many would even see the addition of a "weird complicated foreign game" as a negative (especially if there's an associated trophy/achievement).

So obviously it's no surprise that mahjong was absent, but it's still fun to moan about it.

Overall, though, Sleeping Dogs is an excellent experience - I'd been waiting a year or two for its release and it didn't disappoint. I've been having a lot of fun with it even though I've spent half the time researching and writing a guide for it (my biggest yet, now available from the second link below).