noun-modifying (irregular)
Germanic
Refers broadly to Germanic peoples, languages, or culture. Used attributively in compounds like ゲルマン民族 or ゲルマン語派.
from German Germane
ゲルマン民族の大移動はヨーロッパの歴史を大きく変えた。
The great migration of the Germanic peoples dramatically changed European history.
英語はゲルマン語派に属する。
English belongs to the Germanic language branch.
ドイツ refers specifically to modern Germany, while ゲルマン is a broader historical/linguistic term for Germanic peoples and languages.
From German 'Germane', referring to the Germanic peoples.