That depends on the intent of the sentence, and the intent was only a guess of the GP. But you can analyze だけに in two ways:

英語に吹き替える to dub in English (the base case of 吹き替える)

英語だけに吹き替える to dub just in English (だけ + に)

アメリカだけに吹き替える to dub, just because it's America / as you'd expect of America (だけに grammar https://tanosuke.com/n2-dakeni)