Powerful languages, like nations, thrive on the weakness of other languages. So when it comes to the question of whether or not English is killing other languages, the answer, plain and short, is Yes, it's killing other languages in the same way that every language associated with a nation-state kills other minority languages.
Thai is killing Hmong, Akha, Kuuki Thaadow and other minority .
Russian killed many Uralic and Eskimo-Aleut languages and attempted to kill many of the Turkic languages, like Uzbek and Kazakh, and Caucasian language like Georgian. But the breakup of the USSR and the renationalization of those countries have potentially spared many of them.
And so by the same token, English is killing or has killed hundreds of, including many of the languages in the Algonquian, Iroquoian and Athabaskan families, to name but a few.
Also, in the UK and Ireland, English has killed or come close to killing Celtic, Gaelic and so on. And in Australia, English has killed many Australian aboriginal languages.
So, ultimately, languages associated with a nation-state will kill the other minority languages as a function of.
- nationalized schools, where success is determined by knowing the dominant language
- centralized government, where knowing the dominant language is crucial to finding a job
- social pressure to fit in
- urban migration, removing many of the barriers to assimilation
It worth noting that a number of countries and organizations have tried to avoid this state of affairs. India recognizes several dozen languages in its constitution, which is an important step forward. Australia and New Zealand have been making efforts to support Maori languages. Universities and organizations in the US, such asare attempting to help Native American tribes maintain their languages.
The other answers to this question are suggesting other effects of encroaching English, however, and that, I think, is far overstated. France will never become an English speaking country. Neither will Thailand, Russia, China or any other country that isn't English speaking already. Indeed, I can't think of a single instance, absent conquest, where some language overran another nationalized language.
So, English may yet kill all the other languages in the UK, Australia, the US and other places where it's the main language; all the other minority languages in the world may be wiped out by the dominant languages in their country; we may face the sad fate of being left with only a few languages per country, i.e., several hundred. But so long as countries exist, the English language won't encroach further even though American culture might.
While the idea of language death is starting to get more publicity, it's important to know what it really means. It's not about English computer terms ruining the purity of French or too much gosh darned loud American rock and roll. It's about the disappearance of minority languages around the globe.