The reason that the
Mandarin name for
McDonald's is "Mai dang lao" is because of
Cantonese. McDonald's came first to
Hong Kong, where they used the characters for wheat, serve, and work, which in
Cantonese are pronounced "Mak dang lo," which sounds significantly closer to the
English pronunciation. Afterwards, the same characters (with the Mandarin pronunciation) were used for the Mandarin name of McDonald's, which is why "Mai dang lao" doesn't really sound very close to English.
This is also why in Mandarin, Pizza Hut is called "Bi sheng ke" - because in Cantonese the pronunciation is "Pi sang hak," and they just used the same characters.
Another example is the snack food Pocky, which is pronounced "bak hei" in Cantonese, but becomes "bai qi" in Mandarin.