Cantonese and Mandarin are written the same.

I’m serious. A Cantonese speaker and a Mandarin speaker both read the same Chinese. But how they pronounce what they’re reading is totally different (and mutually unintelligible.) For example: I’ve been paying attention to symbols (especially simple ones) and I see this one a lot:

It’s the symbol for “up”. In German it’d be “auf”. In Spanish, “arriba”. I know it means “up”, but have no idea what the words would be in Mandarin or Cantonese.

Another example is this symbol: 44. (English: forty-four. German: vierundvierzig. Russian: Sorog-chitirye.) The meaning stays the same, but depending on what language you speak, it’ll be spoken completely differently.

“How is this possible?!” you exclaim. As with a symbol or picture of anything, there are no pronunciation cues, just meaning cues. Show a picture of a cat to a Greek, a Spaniard and a Hungarian and they’ll all call it different things.

So a Mandarin speaker and a Cantonese speaker can’t understand each other speaking, but they could write and understand each other.

To thicken the plot, Chinese is written either simplified or traditional. Here are a few examples I just grabbed: