I suspect it would only work in the USA.
I am not sure of other countries using 911.
True enough, most other countries have their own unique emergency numbers.
However, on GSM phone systems (more or less the world standard), 112 is used as a universal number that automatically connects to 911, 999 or whatever the appropriate local number is. Even the US, where the GSM carriers are AT&T & T-Mobile. (I am not sure if the CDMA phone standard shares this protocol.)
Whether someone who speaks English will be available at the other end of the line is another matter.