That sounds really interesting. Your user name suggests your a German speaker. Is d English and old Germanic similar
English isn't really comparable to any old language, while at the same time being very comparable to most old languages. Take pigs for example:
Swine - the English collective term for many pigs or the general descriptor for animals of the pig family. Stems from the German "Schwein" which just means pig.
Pork - the English term for pig meat. Stems from the French "Porc" which, in turn stems from the Latin for pig which is "Porcum".
You get a similar situation with cows:
Cow - Stems from the german "Kuh" (or "cu" in ye olde currency)
Beef - Stems from the French "Boeuf" which in turn stems from the Latin "bos".
Because, as the words tell you, in England for many years the French ate what the Germans provided
(ie: the French were the ruling class and the Germans were the working class). So, to answer your question, yes, between about 650AD and 1000AD English would have been virtually the same language as German, however, once the French took over (1066AD) they also took over the power of the word, and we all know what the French are like when it comes to language, so most texts were forthwith produced in Latin/French.
The story of the first Bible to be written in English (early 1500s) is a fascinating story of bloodshed and rebellion and ties in with the equally fascinating and bloody story of the famous German Luther. The upshot of which was an England determined to become it's own identity away from natural rivalries in Europe and the English scholars started making English the default national language, a hodgepodge of mainly Germanic and French but undeniably something of it's own identity.