Twain's Running Gag of being a Grammar Nazi toward Wang makes a lot more sense when you learn that he raised him. This means that not only has Twain been putting up with Wang's You No Take Candle style of speech for years, but that Wang has been apparently doing it on purpose the whole time, as he was actually raised in an English speaking environment.
Not necessarily. It's stated that Wang owns quite a lot of farm land in China, so he probably spends a decent amount of his time overseeing it. The locals probably speak You No Take Candle, so enough immersion would likely shape Wang's speech. Plus, he hasn't lived with Twain since he was 19, which was many years ago.
It could be due to the fact that his actor, Truman Capote, is an author and would insist on the grammar being correct.
Twain's "The Reason You Suck" Speech against the detectives takes on new meaning with the ultimate Twist Ending that the mastermind was the maid- since none of the detectives suggested that in any of their various "theories", that has to mean that they all accepted that the maid really had been a mannequin the entire time, despite actually seeing her walk around, meaning they swallowed the most stupid and unlikely "twist" in the whole story instead of the much more plausible explanation that she was real and, since both butler and Twain had been murdered beforehand, that she was most likely the killer. Scratch that- "suck" is too generous for this level of idiocy (though its justified by Rule of Funny of course).
Early hint that the maid is not what she seems (only for viewers, not the characters): She stated she can't read English, still she showed the guests a message, that the butler was murdered.
The ending implies that Twain, Bensonmum, and Yetta are all the same person. However, Bensonmum has scenes with Twain and Yetta where they are shown at the same time and hints that Bensonmum at least is a separate entity. Which means either he vanishes midway through the film or he was murdered. Yet by the end of the film, the detectives don't even seem convinced a murder has taken place at all. This means that Twain/Yetta may have outsmarted them even more than they realize; he murdered his butler, stuck the body right in front of them, and the world's greatest detectives just dismiss it as another Mind Screw.
That's not it. What actually happened was that Yetta is the killer, and she murdered both the butler and Twain. After all, both the butler and Twain show up as corpses, yet the maid pretends she was a mannequin the entire time. Since the detectives buy this and don't think any murder was committed (apart from a "very good weekend", of course), this really does come back to them just being idiots, with the maid either being just as stupid (for thinking that would work- and thus lucky that it did) or smart enough to realize just how stupid all of the detectives actually are and know they would be dumb enough to swallow that she was really a mannequin.
Alternately, neither Bensonmum nor Twain died, they simply faked their deaths with mannequins. The maid and butler in particular have no reason to fake their interactions between each other, as neither knew the other beforehand, making the maid's language cards redundant if she knew he was blind (as she'd have to in order to impersonate him). It's better to chalk all these events up to Rule of Funny, or Bellisario's Maxim.
The most scathing parodies in the movie are set less on the novels than popular conceptions from their movie adaptations. Sam Diamond's, for instance, also includes a series of unsubtle Take Thats directed at Humphrey Bogart and gumshoe detectives in general, rather than Sam Spade in specific, due to the general perception that Bogart was typecast. Despite Bogart looking nothing like the literary character of Spade, and only ever playing the character in The Maltese Falcon, Bogart's popularly considered the definitive version. Similarly, Diamond's comment that he only has the one jacket is a reference to the perceived Limited Wardrobe of Bogart's detectives, who tended to wear tuxes, cheap suits, and raincoats.
