[Even ca. 700-1000 A.D., Old English and the ancestors of modern German (modern 'Hoch Deutsch') were pretty different, if obviously related, e.g.:

Old English:

============

Fæder ūre, ðū ðē eart on heofonum,

Sī ðīn nama gehālgod.

Tō becume ðīn rice.

Gewurde ðīn willa

On eorþan swā swā on heofonum.

Urne gedæghwamlīcan hlāf syle ūs tōdæg.

And forgyf ūs ūre gyltas,

Swā swā wē forgyfaþ ūrum gyltendum.

And ne gelæd ðū ūs on costnunge,

ac alȳs ūs of yfele.

* * * *

Old High German (Bavarian):

===========================

Fater unser, du pist in himilum.

Kauuihit si namo din.

Piqhueme rihhi din,

Uuesa din uuillo,

sama so in himile est, sama in erdu.

Pilipi unsraz emizzigaz kip uns eogauuanna.

Enti flaz uns unsro sculdi,

sama so uuir flazzames unsrem scolom.

Enti ni princ unsih in chorunka.

Uzzan kaneri unsih fona allem sunton.

Is there a continental European Germanic language that was closer to English at that time? An ancestor of modern Frisian or something?

Fadar usa firiho barno,

thu bist an them hohon himila rikea,

geuuihid si thin namo uuordo gehuuilico,

Cuma thin craftag riki.

UUerða thin uuilleo oƀar thesa werold alla,

so sama an erðo, so thar uppa ist

an them hohon himilo rikea.

Gef us dag gehuuilikes rad, drohtin the godo,

thina helaga helpa, endi alat us, heƀenes uuard,

managoro mensculdio,

al so uue oðrum mannum doan.

Ne lat us farledean leða uuihti

so forð an iro uuileon, so uui uuirðige sind,

ac help us uuiðar allun uƀilon dadiun.

[these are all of course translations from Latin, so there are also differences in translator choices as well.]

Thanks for the Old Saxon example. Very interesting!