Contrary to what you may think, Chow Yun Fat is very well spoken. He's got a very good grasp of the English language with something of an accent, not too thick, but very understandable. And you should actually blame Hollywood and the film industry for these guys not getting the roles they may want. It's not always up to them to decide what kind of roles they play. They've become typecasted as action stars and movie studios here and in Hong Kong don't particularly like them straying from that.
For instance, Jackie Chan had an idea for a dramatic movie and was pushing it to the studios, but they feared it wouldn't sell with the people, so they threatened to pull funding unless he added action to it, at the cost of the story. That movie ended up being Gorgeous. It was decent, but forgettable.
It's not always their faults they can't get the roles they want, you forget that the studios already see them as two-dimensional action stars, and in the case of Jackie Chan buddy comedy action movies, that it's the only type of movies they can be halfway successful in, so they're not gonna take a risk at that.
Chow Yun Fat's lucky in that he transcended his dual-gun blazing persona early on because he did both dramatic and action roles. He had the chops to be intense and emotive, so he's done well with himself. Jacky Chan and Jet Li, on the other hand, never really had chances to be taken seriously in dramatic roles since they'd done nothing but action and martial arts movies since the beginning of their careers. And that's just their Hong Kong career, they've only been doing movies here since about 1998. So, it hasn't been so long.
Another thing is the racial card. It sucks and I don't want to pull it, but it still exists. How many widely released movies have an Asian as the main character? A movie that isn't being made by an Asian computer that is funded by Hollywood? We saw a couple back in the day, the Corruptor, the Tuxedo, Romeo Must Die, the Medallion, Shanghai Noon, Rush Hour, the One. And even then, most of these movies were buddy flicks, too. And in some cases, like Romeo Must Die or the Tuxedo, you never get to see the main character get the girl, right? There's this invisible hand holding everything back, because the studios just don't think audiences are ready to see that. Granted, this was a couple years ago, so maybe it's changed, but the studios continual pushing of these types of roles drove them mad. Jackie Chan took time off because he was getting frustrated wtih studios messing with the way he filmed, Chow Yun Fat took off because he was tired of getting crappy movie parts. It's not entirely their fault that they don't get the roles they want, you know?
And inability to speak the language? I think that's a ridiculous reason. They can speak English perfectly well, I mean, sure it comes makes them come off as really fobby, but that's not their fault. It wouldn't make any difference if they spoke perfect English, what holds them back is the accent. They were all born and raised in Hong Kong and China and learned English later on in their lives after becoming more well-known. Their accent is something that's never gonna go away, no matter how much English lessons they'll get. So, I think your argument is flawed. They can speak English and they have proved it in all the movies they've done over here. I mean, watch an interview or two of them and you can see they can understand and communicate perfectly fine in an English environment. Chow Yun Fat, though, is the luckier one as his accent is much less pronounced.
Hmm, I seem to have gone on a rather long tirade. Apologies for the tone, by the way. I guess this is one of the few things that can get me worked up, haha.