• I just looked over some of the recent scanslations for Lau's voice and, er, well. I think it's pretty obvious to anyone who follows the scanslations that I'm not using them for his voice; in the scanslations, he's very rough and casual.
• When I was reading it through in Japanese (though, do note that my Japanese isn't the best), I didn't notice anything distinctive about Lau's speech patterns other than his tendency to call people by their titles; obviously this is difficult to duplicate in Micro, as he doesn't use names but there are no ranks to go by here, but. That's his verbal quirk.
• He does speak casually. He uses dictionary forms rather than -ます; I should note, though, that Ciel does as well, and his speech isn't translated as slangily as Lau's is. I interpret Lau's casual speech style as a kind of arrogance rather than a verbal quirk-- he's basically implying that he's equal to an earl (which, of course, he is in many ways, being apparently fairly high in the Chinese mafia).
• Likewise, I interpret his "why so formal?" at Ciel in chapter 15 to be in reference to Ciel referring to him as a member of said mafia rather than speech patterns. I'm not entirely sure if this influenced the scanslation team at all, but I did feel it deserves some note. (IIRC, Ciel isn't using formal speech patterns in that exchange, either.)
• All that said, I'm a lot more comfortable with him and am going to play with his speech patterns a little bit until they feel "on" for me-- since I'm not relying on the scanslators to give me a sense of what his speech patterns would be like in English, I have to do some more legwork myself to make it Lau. I think I've been slipping a little formal even though the exchanges haven't been so much, and I need to fix that. Basically, I feel that he's very casual, but not overly so. Though, again, I am not an expert at Japanese, so second/third/fourth opinions are welcome.