In which countries is English spoken?
Just about all of them
English is spoken as the native language in countries such as English. It's spoken as the language of colonization and settlement in other countries such as Nigeria. It also is spoken as the second language of choice in required language learning in schools in such countries as the Netherlands and Portugal. And it's spoken as the official language in countries such as India where the linguistic situation is so explosive as to preclude one native…
I wouldn't say that 'most countries speak English' as they have their own languages. It's more that many people in many countries speak English, whether as a first or second language. The spread of the British Empire seeded the use of English in many places, and today it has become economically advantageous to be able to communicate in English, not least because it is the language of many of the world's largest economies.