Linguists hate the idea of "langugage death" -- what happens when people no longer speak a language. Following from the idea of language death is the idea of killer languages -- languages that cause other languages to die. You can argue that English is or is not a killer language.
You can say it is because so many people in the world now speak English even in places where it is not the native language. You can argue that this makes them speak their own language less and it starts to kill their own language.
But you can also say English is not a killer language (not anymore, since it has killed off the other languages in the United States, Australia, Great Britain, etc). People in China, for example, do not stop speaking their language because of English -- they simply learn English in addition to their own.
All big languages are killers -- they kill off the little regional languages and dialects in their own areas. English has already done this, but it cannot kill other major languages and it is not responsible for the death of little languages in other areas (where English is not the native language).