Keep in mind both the English and German names come from Latin norinberga. The <e> is just reduction of the back i-vowel in an unstressed position in English, which was lost in German. The <n> is assimilated to match the following <b> but is preserved in the German. It is also worth mentioning that German <ü> was the result of an umlaut vowel shift. Pretty standard. None of this is an unusual phonological development.