The word god is not germanic, like you said in Gemanic the word is Gudan, not god. Gudan means to call, but God is not gudan. God only exists in English.
Not strictly true.
The modern German word for 'God' is 'Gott' - the German and English languages are littered with examples of words where the letters 'd' and 't' are interchangeable. The history of the two languages can, amongst other things, be traced to the dead language 'Sanskrit'
So yes, 'God' in the written language is a reasonably modern construct but the word as 'idea' in the spoken languag eis considerably older.
Best Wishes
David