Why does it need any statistics to prove?
If a person lives in Taiwan but only speaks English, he could get tons of Taiwanese who speak English to socialize with. Even some shopkeepers in 7-11 speak decent English.
Not being able to speak the local language doesn’t affect much to that person.
On the contrary, if a person lives in the U.S., Canada, the U.K., Ireland, Australia, New Zealand, etc, but only speaks Mandarin or Taiwanese, the only place where he could possibly find someone to communicate with is the local Chinese/Taiwanese neighborhood/community. Not being able to speak the local language affects badly to that person.
How many Westerners speak Mandarin or Taiwanese?
How many non-Westerners speak English?
It’s so obvious.