English belongs to the West Germanic family tree. There are a lot of different options about which language is the closet to English. However, Semantically Scots is the closest to English.
Moreover, English originated from Fris which is a language spoken in the northern province of the Netherlands called "Friesland". Fris is still being spoken in the Netherlands.
Furthermore, English had large influence on Latin words due to the occupation of the French in England during the middle ages.
It is hard to say which language is closest as it is a mix of Germanic, Latin, French, and even greek.