What was Big Willy Shakes going for?
Mistress Quickly is famous for all the wrong reasons. Everyone knows about her habit of accidentally talking dirty, which makes her look silly and shady—like when says that Mistress Ford's servants "mistook their erection" when she means to say they misunderstood their directions (3.5.34-35). Whoops. Talk about sticking your foot in your mouth.
Shakespeare has a lot of fun at Mistress Quickly's expense. Mistress Quickly obviously has no formal education. How could she? Most women and lower-class servants didn't get to go to school. Because of all this, she's an outsider in the middle-class world of the play. But, one thing she's an insider on is speaking English.
This whole speech makes way more sense when you know that Caius is the bad-tempered French doctor who wants to marry Anne Page. He's also Mistress Quickly's verbally abusive boss and could definitely use a session or two of anger management class. Notice how he's always running around picking fights, making outrageous threats, and screaming "by gar!" (a.k.a. "by god!").
We know what you're thinking: "By gar! What's up with the thick accent?" Good question, Shmoopers; we're glad you asked. Caius's status as a foreigner makes him an outsider and the butt of a lot of jokes in this play, like when he uses the word "turd" when he means to say "third" (3.3.200). Oops.
In fact, The Host of the Garter Inn spends an entire scene ragging on Caius's French accent and insulting him by using a bunch of English slang that the guy doesn't understand. So even though Mistress Quickly is one big joke herself, she's got it together compared to the silly old French guy. Even if everyone makes fun of her, at least she can make fun of him.
Why is Shakespeare so hell bent on making the Frenchman look foolish? Well, Shakespeare is all about trying to give us a snapshot of small town English life. In the process of trying to define what it means to be English, Shakespeare often uses foreigners like Caius to show us what Englishness isn't. The end result? A play that ends up looking a smidge xenophobic. Sorry, Shakey.
Mistress Quickly's line is an example of this. She's complaining about Caius' lack of proper English (king's English) because he messes it up all the time. The irony is, she makes accidental puns and mistakes all the time. It's just not allowed when it's a foreigner. See what we mean about xenophobic?
A funny tidbit about this saying is that Shakespeare wrote this play when a queen (Elizabeth I) was on the throne, but Quickly says king's English. How come? Well, in the world of the play, a king (Henry V) is on the throne. So he had to adapt it. He's a clever one, that Shakespeare.