Is Dutch an English language?

There is only one "English language" and that's English.

English and Dutch belong to a family of languages known as the Germanic languages. These also include German (obviously!), Danish, Swedish, Norwegian and Afrikaans (which is very similar to Dutch).

Dutch is probably the second-closest relative to English. It is sort of part-German and part-English, but sounds closer to German. It also has many features of its own, such as the weird vowel sounds ("ij" and "ui") and guttural consonents. The Frisian language, which is spoken in the northern part of the Netherlands, is the closest relative to English.