I have previously written about Wrong MTR station names and the Hong Kong Free Press has an interesting article on a similar theme

Foreign influence Part 1: Lost in translation

[..] Mong Kok is another prime example. The former coastal region was named after the overgrown silvergrass found in the area 芒角 mong⁴ gok³, (‘corner of silvergrass’).

When the government reclaimed the bay and developed the area in the early 1900s, the Chinese name was changed to 旺角(wong⁶ gok³) which means “Prosperity Point.”

The English name was never updated.

I remember being told that 芒角 meant "busy" place, but that seems to be another Chinese character 忙with the same Pinyin romanization, which is an understandable error for anyone who didn't check a 19th Century map.  

The author of the HKFP piece seems to be Chinese, so predictably makes a better job of this than I did!