>>17906897 (OP)
The further back you go, the closer they get. Anglo-Saxons in Britain and Vikings could communicate without much effort and there's a pretty good continuum from Dutch to German to Frisian, etc....but the "Anglo" link jumped to the British Isles and morphed on its own, as island tend to do to things. Even up to the time of Shakespeare, English grammar and spelling was quite "German", as was the vocabulary. I still think "how would Shakespeare say this" to get to a rough German translation.
Du = Thou; Sie = Thee; Deine(r) = Thine, etc.....lots of commonalities if you can speak/read a bit of both languages, and English is a piece of cake for them to learn b/c it's so streamlined of gender, and all the crazy cases, etc....the hardest part about English is the spelling, which is just wacky and part of the charm due to all the influences over the centuries.